Fiber laser with free-space components

ABSTRACT

In one embodiment, a laser system includes a seed laser diode configured to produce a free-space seed-laser beam and a seed-laser lens configured to collimate the seed-laser beam. The laser system also includes a pump laser diode configured to produce a free-space pump-laser beam and a pump-laser lens configured to collimate the pump-laser beam. The laser system further includes an optical-beam combiner configured to combine the collimated seed-laser and pump-laser beams into a combined free-space beam and a focusing lens configured to focus the combined beam. The laser system also includes an optical gain fiber that includes an input end configured to receive the focused beam. The laser system also includes a mounting platform, where one or more of the seed laser, the seed-laser lens, the pump laser, the pump-laser lens, the combiner, the focusing lens, and the input end of the gain fiber are mechanically attached to the platform.

PRIORITY

This application claims the benefit, under 35 U.S.C. § 119(e), of U.S.Provisional Patent Application 62/574,046, filed Oct. 18, 2017, theentirety of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure generally relates to lidar systems.

BACKGROUND

Light detection and ranging (lidar) is a technology that can be used tomeasure distances to remote targets. Typically, a lidar system includesa light source and an optical receiver. The light source can be, forexample, a laser which emits light having a particular operatingwavelength. The operating wavelength of a lidar system may lie, forexample, in the infrared, visible, or ultraviolet portions of theelectromagnetic spectrum. The light source emits light toward a targetwhich then scatters the light. Some of the scattered light is receivedback at the receiver. The system determines the distance to the targetbased on one or more characteristics associated with the returned light.For example, the system may determine the distance to the target basedon the time of flight of a returned light pulse.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example light detection and ranging (lidar)system.

FIG. 2 illustrates an example scan pattern produced by a lidar system.

FIG. 3 illustrates an example lidar system with an example overlapmirror.

FIG. 4 illustrates an example lidar system with an example rotatingpolygon mirror.

FIG. 5 illustrates an example light-source field of view and receiverfield of view for a lidar system.

FIG. 6 illustrates an example scan pattern that includes multiple scanlines and multiple pixels.

FIG. 7 illustrates an example unidirectional scan pattern 200.

FIG. 8 illustrates an example seed laser that includes a laser diodedriven by a pulse generator.

FIG. 9 illustrates an example seed laser with multiple laser diodes thatare combined together by a multiplexer.

FIG. 10 illustrates an example light source that includes a seed laserand an amplifier.

FIG. 11 illustrates an example double-pass fiber-optic amplifier.

FIG. 12 illustrates an example spectrum of an optical signal before andafter passing through a filter.

FIG. 13 illustrates an example single-pass fiber-optic amplifier.

FIG. 14 illustrates an example booster amplifier that produces afree-space output beam.

FIG. 15 illustrates a top view of an example free-space pre-amplifierassembly.

FIG. 16 illustrates an example mechanical-attachment technique based onactive alignment of an optical component.

FIG. 17 illustrates an example mechanical-attachment technique based onpassive alignment of an optical component.

FIG. 18 illustrates a top view of an example free-spacebooster-amplifier assembly.

FIG. 19 illustrates an example light source that includes a free-spacepre-amplifier assembly and a free-space booster-amplifier assembly.

FIG. 20 illustrates an example fiber-optic amplifier with two pump laserdiodes.

FIG. 21 illustrates an example fiber-optic booster amplifier with twopump laser diodes.

FIG. 22 illustrates a top view of an example free-space amplifierassembly with two pump laser diodes.

FIG. 23 illustrates an example absorption spectrum for anerbium/ytterbium gain fiber.

FIG. 24 illustrates an example lookup table for adjusting pump-lasercurrent based on temperature.

FIG. 25 illustrates an example method for adjusting the optical powerprovided by pump lasers in an optical amplifier.

FIG. 26 illustrates an example computer system.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 illustrates an example light detection and ranging (lidar) system100. In particular embodiments, a lidar system 100 may be referred to asa laser ranging system, a laser radar system, a LIDAR system, a lidarsensor, a laser detection and ranging (LADAR or ladar) system, a sensor,or a sensor head. In particular embodiments, a lidar system 100 mayinclude a light source 110, mirror 115, scanner 120, receiver 140, orcontroller 150. The light source 110 may be, for example, a laser whichemits light having a particular operating wavelength in the infrared,visible, or ultraviolet portions of the electromagnetic spectrum. As anexample, light source 110 may include a laser with an operatingwavelength between approximately 1.2 μm and 1.7 μm. The light source 110emits an output beam of light 125 which may be continuous-wave, pulsed,or modulated in any suitable manner for a given application. The outputbeam of light 125 is directed downrange toward a remote target 130. Asan example, the remote target 130 may be located a distance D ofapproximately 1 m to 1 km from the lidar system 100.

Once the output beam 125 reaches the downrange target 130, the targetmay scatter or reflect at least a portion of light from the output beam125, and some of the scattered or reflected light may return toward thelidar system 100. In the example of FIG. 1, the scattered or reflectedlight is represented by input beam 135, which passes through scanner 120and is directed by mirror 115 to receiver 140. In particularembodiments, a relatively small fraction of the light from output beam125 may return to the lidar system 100 as input beam 135. As an example,the ratio of input beam 135 average power, peak power, or pulse energyto output beam 125 average power, peak power, or pulse energy may beapproximately 10⁻¹, 10⁻², 10⁻³, 10⁻⁴, 10⁻⁵, 10⁻⁶, 10⁻⁷, 10⁻⁸, 10⁻⁹,10⁻¹⁰, 10⁻¹¹, or 10⁻¹². As another example, if a pulse of output beam125 has a pulse energy of 1 microjoule (μJ), then the pulse energy of acorresponding pulse of input beam 135 may have a pulse energy ofapproximately 10 nanojoules (nJ), 1 nJ, 100 picojoules (pJ), 10 pJ, 1pJ, 100 femtojoules (fJ), 10 fJ, 1 fJ, 100 attojoules (aJ), 10 aJ, 1 aJ,or 0.1 aJ. In particular embodiments, output beam 125 may be referred toas a laser beam, light beam, optical beam, emitted beam, or beam. Inparticular embodiments, input beam 135 may be referred to as a returnbeam, received beam, return light, received light, input light,scattered light, or reflected light. As used herein, scattered light mayrefer to light that is scattered or reflected by a target 130. As anexample, an input beam 135 may include: light from the output beam 125that is scattered by target 130; light from the output beam 125 that isreflected by target 130; or a combination of scattered and reflectedlight from target 130.

In particular embodiments, receiver 140 may receive or detect photonsfrom input beam 135 and generate one or more representative signals. Forexample, the receiver 140 may generate an output electrical signal 145that is representative of the input beam 135. This electrical signal 145may be sent to controller 150. In particular embodiments, controller 150may include a processor, computing system (e.g., an ASIC or FPGA), orother suitable circuitry. A controller 150 may be configured to analyzeone or more characteristics of the electrical signal 145 from thereceiver 140 to determine one or more characteristics of the target 130,such as its distance downrange from the lidar system 100. This can bedone, for example, by analyzing the time of flight or phase modulationfor a beam of light 125 transmitted by the light source 110. If lidarsystem 100 measures a time of flight of T (e.g., T represents around-trip time of flight for an emitted pulse of light to travel fromthe lidar system 100 to the target 130 and back to the lidar system100), then the distance D from the target 130 to the lidar system 100may be expressed as D=c·T/2, where c is the speed of light(approximately 3.0×10⁸ m/s). As an example, if a time of flight ismeasured to be T=300 ns, then the distance from the target 130 to thelidar system 100 may be determined to be approximately D=45.0 m. Asanother example, if a time of flight is measured to be T=1.33 μs, thenthe distance from the target 130 to the lidar system 100 may bedetermined to be approximately D=199.5 m. In particular embodiments, adistance D from lidar system 100 to a target 130 may be referred to as adistance, depth, or range of target 130. As used herein, the speed oflight c refers to the speed of light in any suitable medium, such as forexample in air, water, or vacuum. As an example, the speed of light invacuum is approximately 2.9979×10⁸ m/s, and the speed of light in air(which has a refractive index of approximately 1.0003) is approximately2.9970×10⁸ m/s.

In particular embodiments, light source 110 may include a pulsed laser.As an example, light source 110 may be a pulsed laser configured toproduce or emit pulses of light with a pulse duration or pulse width ofapproximately 10 picoseconds (ps) to 20 nanoseconds (ns). As anotherexample, light source 110 may be a pulsed laser that produces pulseswith a pulse duration of approximately 1-5 ns. As another example, lightsource 110 may be a pulsed laser that produces pulses at a pulserepetition frequency of approximately 100 kHz to 5 MHz or a pulse period(e.g., a time between consecutive pulses) of approximately 200 ns to 10μs. In particular embodiments, light source 110 may have a substantiallyconstant pulse repetition frequency, or light source 110 may have avariable or adjustable pulse repetition frequency. As an example, lightsource 110 may be a pulsed laser that produces pulses at a substantiallyconstant pulse repetition frequency of approximately 640 kHz (e.g.,640,000 pulses per second), corresponding to a pulse period ofapproximately 1.56 μs. As another example, light source 110 may have apulse repetition frequency that can be varied from approximately 500 kHzto 3 MHz. As used herein, a pulse of light may be referred to as anoptical pulse, a light pulse, or a pulse.

In particular embodiments, light source 110 may produce a free-spaceoutput beam 125 having any suitable average optical power, and theoutput beam 125 may have optical pulses with any suitable pulse energyor peak optical power. As an example, output beam 125 may have anaverage power of approximately 1 milliwatt (mW), 10 mW, 100 mW, 1 watt(W), 10 W, or any other suitable average power. As another example,output beam 125 may include pulses with a pulse energy of approximately0.01 μJ, 0.1 μJ, 1 μJ, 10 μJ, 100 μJ, 1 mJ, or any other suitable pulseenergy. As another example, output beam 125 may include pulses with apeak power of approximately 10 W, 100 W, 1 kW, 5 kW, 10 kW, or any othersuitable peak power. The peak power (P_(peak)) of a pulse of light canbe related to the pulse energy (E) by the expression E=P_(peak)·Δt,where Δt is the duration of the pulse, and the duration of a pulse maybe defined as the full width at half maximum duration of the pulse. Forexample, an optical pulse with a duration of 1 ns and a pulse energy of1 μJ has a peak power of approximately 1 kW. The average power (P_(av))of an output beam 125 can be related to the pulse repetition frequency(PRF) and pulse energy by the expression P_(av)=PRF·E. For example, ifthe pulse repetition frequency is 500 kHz, then the average power of anoutput beam 125 with 1-μJ pulses is approximately 0.5 W.

In particular embodiments, light source 110 may include a laser diode,such as for example, a Fabry-Perot laser diode, a quantum well laser, adistributed Bragg reflector (DBR) laser, a distributed feedback (DFB)laser, or a vertical-cavity surface-emitting laser (VCSEL). As anexample, light source 110 may include an aluminum-gallium-arsenide(AlGaAs) laser diode, an indium-gallium-arsenide (InGaAs) laser diode,or an indium-gallium-arsenide-phosphide (InGaAsP) laser diode. Inparticular embodiments, light source 110 may include a pulsed laserdiode with a peak emission wavelength of approximately 1400-1600nanometers (nm). As an example, light source 110 may include a laserdiode that is current modulated to produce optical pulses. In particularembodiments, light source 110 may include a pulsed laser diode followedby one or more optical-amplification stages. As an example, light source110 may be a fiber-laser module that includes a current-modulated laserdiode with a peak wavelength of approximately 1550 nm followed by asingle-stage or a multi-stage erbium-doped fiber amplifier (EDFA). Asanother example, light source 110 may include a continuous-wave (CW) orquasi-CW laser diode followed by an external optical modulator (e.g., anelectro-optic modulator), and the output of the modulator may be fedinto an optical amplifier.

In particular embodiments, an output beam of light 125 emitted by lightsource 110 may be a collimated optical beam with any suitable beamdivergence, such as for example, a divergence of approximately 0.5 to5.0 milliradians (mrad). A divergence of output beam 125 may refer to anangular measure of an increase in beam size (e.g., a beam radius or beamdiameter) as output beam 125 travels away from light source 110 or lidarsystem 100. In particular embodiments, output beam 125 may have asubstantially circular cross section with a beam divergencecharacterized by a single divergence value. As an example, an outputbeam 125 with a circular cross section and a divergence of 2 mrad mayhave a beam diameter or spot size of approximately 20 cm at a distanceof 100 m from lidar system 100. In particular embodiments, output beam125 may be an astigmatic beam or may have a substantially ellipticalcross section and may be characterized by two divergence values. As anexample, output beam 125 may have a fast axis and a slow axis, where thefast-axis divergence is greater than the slow-axis divergence. Asanother example, output beam 125 may be an astigmatic beam with afast-axis divergence of 4 mrad and a slow-axis divergence of 2 mrad.

In particular embodiments, an output beam of light 125 emitted by lightsource 110 may be unpolarized or randomly polarized, may have nospecific or fixed polarization (e.g., the polarization may vary withtime), or may have a particular polarization (e.g., output beam 125 maybe linearly polarized, elliptically polarized, or circularly polarized).As an example, light source 110 may produce linearly polarized light,and lidar system 100 may include a quarter-wave plate that converts thislinearly polarized light into circularly polarized light. The circularlypolarized light may be transmitted as output beam 125, and lidar system100 may receive input beam 135, which may be substantially or at leastpartially circularly polarized in the same manner as the output beam 125(e.g., if output beam 125 is right-hand circularly polarized, then inputbeam 135 may also be right-hand circularly polarized). The input beam135 may pass through the same quarter-wave plate (or a differentquarter-wave plate) resulting in the input beam 135 being converted tolinearly polarized light which is orthogonally polarized (e.g.,polarized at a right angle) with respect to the linearly polarized lightproduced by light source 110. As another example, lidar system 100 mayemploy polarization-diversity detection where two polarizationcomponents are detected separately. The output beam 125 may be linearlypolarized, and the lidar system 100 may split the input beam 135 intotwo polarization components (e.g., s-polarization and p-polarization)which are detected separately by two photodiodes (e.g., a balancedphotoreceiver that includes two photodiodes).

In particular embodiments, lidar system 100 may include one or moreoptical components configured to condition, shape, filter, modify,steer, or direct the output beam 125 or the input beam 135. As anexample, lidar system 100 may include one or more lenses, mirrors,filters (e.g., bandpass or interference filters), beam splitters,polarizers, polarizing beam splitters, wave plates (e.g., half-wave orquarter-wave plates), diffractive elements, or holographic elements. Inparticular embodiments, lidar system 100 may include a telescope, one ormore lenses, or one or more mirrors to expand, focus, or collimate theoutput beam 125 to a desired beam diameter or divergence. As an example,the lidar system 100 may include one or more lenses to focus the inputbeam 135 onto an active region of receiver 140. As another example, thelidar system 100 may include one or more flat mirrors or curved mirrors(e.g., concave, convex, or parabolic mirrors) to steer or focus theoutput beam 125 or the input beam 135. For example, the lidar system 100may include an off-axis parabolic mirror to focus the input beam 135onto an active region of receiver 140. As illustrated in FIG. 1, thelidar system 100 may include mirror 115 (which may be a metallic ordielectric mirror), and mirror 115 may be configured so that light beam125 passes through the mirror 115. As an example, mirror 115 (which maybe referred to as an overlap mirror, superposition mirror, orbeam-combiner mirror) may include a hole, slot, or aperture which outputlight beam 125 passes through. As another example, mirror 115 may beconfigured so that at least 80% of output beam 125 passes through mirror115 and at least 80% of input beam 135 is reflected by mirror 115. Inparticular embodiments, mirror 115 may provide for output beam 125 andinput beam 135 to be substantially coaxial so that the two beams travelalong substantially the same optical path (albeit in oppositedirections).

In particular embodiments, lidar system 100 may include a scanner 120 tosteer the output beam 125 in one or more directions downrange. As anexample, scanner 120 may include one or more scanning mirrors that areconfigured to rotate, oscillate, tilt, pivot, or move in an angularmanner about one or more axes. In particular embodiments, a flatscanning mirror may be attached to a scanner actuator or mechanism whichscans the mirror over a particular angular range. As an example, scanner120 may include a galvanometer scanner, a resonant scanner, apiezoelectric actuator, a polygonal scanner, a rotating-prism scanner, avoice coil motor, an electric motor (e.g., a DC motor, a brushless DCmotor, a synchronous electric motor, or a stepper motor), or amicroelectromechanical systems (MEMS) device, or any other suitableactuator or mechanism. In particular embodiments, scanner 120 may beconfigured to scan the output beam 125 over a 5-degree angular range,20-degree angular range, 30-degree angular range, 60-degree angularrange, or any other suitable angular range. As an example, a scanningmirror may be configured to periodically oscillate or rotate back andforth over a 15-degree range, which results in the output beam 125scanning across a 30-degree range (e.g., a Θ-degree rotation by ascanning mirror results in a 2Θ-degree angular scan of output beam 125).In particular embodiments, a field of regard (FOR) of a lidar system 100may refer to an area, region, or angular range over which the lidarsystem 100 may be configured to scan or capture distance information. Asan example, a lidar system 100 with an output beam 125 with a 30-degreescanning range may be referred to as having a 30-degree angular field ofregard. As another example, a lidar system 100 with a scanning mirrorthat rotates over a 30-degree range may produce an output beam 125 thatscans across a 60-degree range (e.g., a 60-degree FOR). In particularembodiments, lidar system 100 may have a FOR of approximately 10°, 20°,40°, 60°, 120°, or any other suitable FOR. In particular embodiments, aFOR may be referred to as a scan region.

In particular embodiments, scanner 120 may be configured to scan theoutput beam 125 (which includes at least a portion of the pulses oflight emitted by light source 110) across a FOR of the lidar system 100.In particular embodiments, scanner 120 may be configured to scan theoutput beam 125 horizontally and vertically, and lidar system 100 mayhave a particular FOR along the horizontal direction and anotherparticular FOR along the vertical direction. As an example, lidar system100 may have a horizontal FOR of 10° to 120° and a vertical FOR of 2° to45°. In particular embodiments, scanner 120 may include a first mirrorand a second mirror, where the first mirror directs the output beam 125toward the second mirror, and the second mirror directs the output beam125 downrange. As an example, the first mirror may scan the output beam125 along a first direction, and the second mirror may scan the outputbeam 125 along a second direction that is substantially orthogonal tothe first direction. As another example, the first mirror may scan theoutput beam 125 along a substantially horizontal direction, and thesecond mirror may scan the output beam 125 along a substantiallyvertical direction (or vice versa). In particular embodiments, scanner120 may be referred to as a beam scanner, optical scanner, or laserscanner.

In particular embodiments, one or more scanning mirrors may becommunicatively coupled to controller 150 which may control the scanningmirror(s) so as to guide the output beam 125 in a desired directiondownrange or along a desired scan pattern. In particular embodiments, ascan pattern (which may be referred to as an optical scan pattern,optical scan path, or scan path) may refer to a pattern or path alongwhich the output beam 125 is directed. As an example, scanner 120 mayinclude two scanning mirrors configured to scan the output beam 125across a 60° horizontal FOR and a 20° vertical FOR. The two scannermirrors may be controlled to follow a scan path that substantiallycovers the 60°×20° FOR. As an example, the scan path may result in apoint cloud with pixels that substantially cover the 60° ×20° FOR. Thepixels may be approximately evenly distributed across the 60°×20° FOR.Alternatively, the pixels may have a particular nonuniform distribution(e.g., the pixels may be distributed across all or a portion of the60°×20° FOR, and the pixels may have a higher density in one or moreparticular regions of the 60°×20° FOR).

In particular embodiments, a light source 110 may emit pulses of lightwhich are scanned by scanner 120 across a FOR of lidar system 100. Oneor more of the emitted pulses of light may be scattered by a target 130located downrange from the lidar system 100, and a receiver 140 maydetect at least a portion of the pulses of light scattered by the target130. In particular embodiments, receiver 140 may be referred to as aphotoreceiver, optical receiver, optical sensor, detector,photodetector, or optical detector. In particular embodiments, lidarsystem 100 may include a receiver 140 that receives or detects at leasta portion of input beam 135 and produces an electrical signal thatcorresponds to input beam 135. As an example, if input beam 135 includesan optical pulse, then receiver 140 may produce an electrical current orvoltage pulse that corresponds to the optical pulse detected by receiver140. As another example, receiver 140 may include one or more avalanchephotodiodes (APDs) or one or more single-photon avalanche diodes(SPADs). As another example, receiver 140 may include one or more PNphotodiodes (e.g., a photodiode structure formed by a p-typesemiconductor and a n-type semiconductor) or one or more PIN photodiodes(e.g., a photodiode structure formed by an undoped intrinsicsemiconductor region located between p-type and n-type regions).Receiver 140 may have an active region or an avalanche-multiplicationregion that includes silicon, germanium, or InGaAs. The active region ofreceiver 140 may have any suitable size, such as for example, a diameteror width of approximately 20-500 μm.

In particular embodiments, receiver 140 may include circuitry thatperforms signal amplification, sampling, filtering, signal conditioning,analog-to-digital conversion, time-to-digital conversion, pulsedetection, threshold detection, rising-edge detection, or falling-edgedetection. As an example, receiver 140 may include a transimpedanceamplifier that converts a received photocurrent (e.g., a currentproduced by an APD in response to a received optical signal) into avoltage signal. The voltage signal may be sent to pulse-detectioncircuitry that produces an analog or digital output signal 145 thatcorresponds to one or more characteristics (e.g., rising edge, fallingedge, amplitude, or duration) of a received optical pulse. As anexample, the pulse-detection circuitry may perform a time-to-digitalconversion to produce a digital output signal 145. The electrical outputsignal 145 may be sent to controller 150 for processing or analysis(e.g., to determine a time-of-flight value corresponding to a receivedoptical pulse).

In particular embodiments, controller 150 may be electrically coupled orcommunicatively coupled to light source 110, scanner 120, or receiver140. As an example, controller 150 may receive electrical trigger pulsesor edges from light source 110, where each pulse or edge corresponds tothe emission of an optical pulse by light source 110. As anotherexample, controller 150 may provide instructions, a control signal, or atrigger signal to light source 110 indicating when light source 110should produce optical pulses. Controller 150 may send an electricaltrigger signal that includes electrical pulses, where each electricalpulse results in the emission of an optical pulse by light source 110.In particular embodiments, the frequency, period, duration, pulseenergy, peak power, average power, or wavelength of the optical pulsesproduced by light source 110 may be adjusted based on instructions, acontrol signal, or trigger pulses provided by controller 150. Inparticular embodiments, controller 150 may be coupled to light source110 and receiver 140, and controller 150 may determine a time-of-flightvalue for an optical pulse based on timing information associated withwhen the pulse was emitted by light source 110 and when a portion of thepulse (e.g., input beam 135) was detected or received by receiver 140.In particular embodiments, controller 150 may include circuitry thatperforms signal amplification, sampling, filtering, signal conditioning,analog-to-digital conversion, time-to-digital conversion, pulsedetection, threshold detection, rising-edge detection, or falling-edgedetection.

In particular embodiments, a lidar system 100 may be used to determinethe distance to one or more downrange targets 130. By scanning the lidarsystem 100 across a field of regard, the system can be used to map thedistance to a number of points within the field of regard. Each of thesedepth-mapped points may be referred to as a pixel or a voxel. Acollection of pixels captured in succession (which may be referred to asa depth map, a point cloud, or a frame) may be rendered as an image ormay be analyzed to identify or detect objects or to determine a shape ordistance of objects within the FOR. As an example, a point cloud maycover a field of regard that extends 60° horizontally and 15°vertically, and the point cloud may include a frame of 100-2000 pixelsin the horizontal direction by 4-400 pixels in the vertical direction.

In particular embodiments, lidar system 100 may be configured torepeatedly capture or generate point clouds of a field of regard at anysuitable frame rate between approximately 0.1 frames per second (FPS)and approximately 1,000 FPS. As an example, lidar system 100 maygenerate point clouds at a frame rate of approximately 0.1 FPS, 0.5 FPS,1 FPS, 2 FPS, 5 FPS, 10 FPS, 20 FPS, 100 FPS, 500 FPS, or 1,000 FPS. Asanother example, lidar system 100 may be configured to produce opticalpulses at a rate of 5×10⁵ pulses/second (e.g., the system may determine500,000 pixel distances per second) and scan a frame of 1000×50 pixels(e.g., 50,000 pixels/frame), which corresponds to a point-cloud framerate of 10 frames per second (e.g., 10 point clouds per second). Inparticular embodiments, a point-cloud frame rate may be substantiallyfixed, or a point-cloud frame rate may be dynamically adjustable. As anexample, a lidar system 100 may capture one or more point clouds at aparticular frame rate (e.g., 1 Hz) and then switch to capture one ormore point clouds at a different frame rate (e.g., 10 Hz). A slowerframe rate (e.g., 1 Hz) may be used to capture one or morehigh-resolution point clouds, and a faster frame rate (e.g., 10 Hz) maybe used to rapidly capture multiple lower-resolution point clouds.

In particular embodiments, a lidar system 100 may be configured tosense, identify, or determine distances to one or more targets 130within a field of regard. As an example, a lidar system 100 maydetermine a distance to a target 130, where all or part of the target130 is contained within a field of regard of the lidar system 100. Allor part of a target 130 being contained within a FOR of the lidar system100 may refer to the FOR overlapping, encompassing, or enclosing atleast a portion of the target 130. In particular embodiments, target 130may include all or part of an object that is moving or stationaryrelative to lidar system 100. As an example, target 130 may include allor a portion of a person, vehicle, motorcycle, truck, train, bicycle,wheelchair, pedestrian, animal, road sign, traffic light, lane marking,road-surface marking, parking space, pylon, guard rail, traffic barrier,pothole, railroad crossing, obstacle in or near a road, curb, stoppedvehicle on or beside a road, utility pole, house, building, trash can,mailbox, tree, any other suitable object, or any suitable combination ofall or part of two or more objects.

In particular embodiments, one or more lidar systems 100 may beintegrated into a vehicle. As an example, multiple lidar systems 100 maybe integrated into a car to provide a complete 360-degree horizontal FORaround the car. As another example, 4-10 lidar systems 100, each systemhaving a 45-degree to 90-degree horizontal FOR, may be combined togetherto form a sensing system that provides a point cloud covering a360-degree horizontal FOR. The lidar systems 100 may be oriented so thatadjacent FORs have an amount of spatial or angular overlap to allow datafrom the multiple lidar systems 100 to be combined or stitched togetherto form a single or continuous 360-degree point cloud. As an example,the FOR of each lidar system 100 may have approximately 1-15 degrees ofoverlap with an adjacent FOR. In particular embodiments, a vehicle mayrefer to a mobile machine configured to transport people or cargo. Forexample, a vehicle may include, may take the form of, or may be referredto as a car, automobile, motor vehicle, truck, bus, van, trailer,off-road vehicle, farm vehicle, lawn mower, construction equipment, golfcart, motorhome, taxi, motorcycle, scooter, bicycle, skateboard, train,snowmobile, watercraft (e.g., a ship or boat), aircraft (e.g., afixed-wing aircraft, helicopter, or dirigible), or spacecraft. Inparticular embodiments, a vehicle may include an internal combustionengine or an electric motor that provides propulsion for the vehicle.

In particular embodiments, one or more lidar systems 100 may be includedin a vehicle as part of an advanced driver assistance system (ADAS) toassist a driver of the vehicle in the driving process. For example, alidar system 100 may be part of an ADAS that provides information orfeedback to a driver (e.g., to alert the driver to potential problems orhazards) or that automatically takes control of part of a vehicle (e.g.,a braking system or a steering system) to avoid collisions or accidents.A lidar system 100 may be part of a vehicle ADAS that provides adaptivecruise control, automated braking, automated parking, collisionavoidance, alerts the driver to hazards or other vehicles, maintains thevehicle in the correct lane, or provides a warning if an object oranother vehicle is in a blind spot.

In particular embodiments, one or more lidar systems 100 may beintegrated into a vehicle as part of an autonomous-vehicle drivingsystem. As an example, a lidar system 100 may provide information aboutthe surrounding environment to a driving system of an autonomousvehicle. An autonomous-vehicle driving system may include one or morecomputing systems that receive information from a lidar system 100 aboutthe surrounding environment, analyze the received information, andprovide control signals to the vehicle's driving systems (e.g., steeringwheel, accelerator, brake, or turn signal). As an example, a lidarsystem 100 integrated into an autonomous vehicle may provide anautonomous-vehicle driving system with a point cloud every 0.1 seconds(e.g., the point cloud has a 10 Hz update rate, representing 10 framesper second). The autonomous-vehicle driving system may analyze thereceived point clouds to sense or identify targets 130 and theirrespective locations, distances, or speeds, and the autonomous-vehicledriving system may update control signals based on this information. Asan example, if lidar system 100 detects a vehicle ahead that is slowingdown or stopping, the autonomous-vehicle driving system may sendinstructions to release the accelerator and apply the brakes.

In particular embodiments, an autonomous vehicle may be referred to asan autonomous car, driverless car, self-driving car, robotic car, orunmanned vehicle. In particular embodiments, an autonomous vehicle mayrefer to a vehicle configured to sense its environment and navigate ordrive with little or no human input. As an example, an autonomousvehicle may be configured to drive to any suitable location and controlor perform all safety-critical functions (e.g., driving, steering,braking, parking) for the entire trip, with the driver not expected tocontrol the vehicle at any time. As another example, an autonomousvehicle may allow a driver to safely turn their attention away fromdriving tasks in particular environments (e.g., on freeways), or anautonomous vehicle may provide control of a vehicle in all but a fewenvironments, requiring little or no input or attention from the driver.

In particular embodiments, an autonomous vehicle may be configured todrive with a driver present in the vehicle, or an autonomous vehicle maybe configured to operate the vehicle with no driver present. As anexample, an autonomous vehicle may include a driver's seat withassociated controls (e.g., steering wheel, accelerator pedal, and brakepedal), and the vehicle may be configured to drive with no one seated inthe driver's seat or with little or no input from a person seated in thedriver's seat. As another example, an autonomous vehicle may not includeany driver's seat or associated driver's controls, and the vehicle mayperform substantially all driving functions (e.g., driving, steering,braking, parking, and navigating) without human input. As anotherexample, an autonomous vehicle may be configured to operate without adriver (e.g., the vehicle may be configured to transport humanpassengers or cargo without a driver present in the vehicle). As anotherexample, an autonomous vehicle may be configured to operate without anyhuman passengers (e.g., the vehicle may be configured for transportationof cargo without having any human passengers onboard the vehicle).

FIG. 2 illustrates an example scan pattern 200 produced by a lidarsystem 100. A scan pattern 200 (which may be referred to as a scan) mayrepresent a path or course followed by output beam 125 as it is scannedacross all or part of a FOR. Each traversal of a scan pattern 200 maycorrespond to the capture of a single frame or a single point cloud. Inparticular embodiments, a lidar system 100 may be configured to scanoutput optical beam 125 along one or more particular scan patterns 200.In particular embodiments, a scan pattern 200 may scan across anysuitable field of regard (FOR) having any suitable horizontal FOR(FOR_(H)) and any suitable vertical FOR (FOR_(V)). For example, a scanpattern 200 may have a field of regard represented by angular dimensions(e.g., FOR_(H)×FOR_(V)) 40°×30°, 90°×40°, or 60°×15°. As anotherexample, a scan pattern 200 may have a FOR_(H) greater than or equal to10°, 25°, 30°, 40°, 60°, 90°, or 120°. As another example, a scanpattern 200 may have a FOR_(V) greater than or equal to 2°, 5°, 10°,15°, 20°, 30°, or 45°. In the example of FIG. 2, reference line 220represents a center of the field of regard of scan pattern 200. Inparticular embodiments, reference line 220 may have any suitableorientation, such as for example, a horizontal angle of 0° (e.g.,reference line 220 may be oriented straight ahead) and a vertical angleof 0° (e.g., reference line 220 may have an inclination of 0°), orreference line 220 may have a nonzero horizontal angle or a nonzeroinclination (e.g., a vertical angle of +10° or −10°. In FIG. 2, if thescan pattern 200 has a 60°×15° field of regard, then scan pattern 200covers a ±30° horizontal range with respect to reference line 220 and a±7.5° vertical range with respect to reference line 220. Additionally,optical beam 125 in FIG. 2 has an orientation of approximately −15°horizontal and +3° vertical with respect to reference line 220. Opticalbeam 125 may be referred to as having an azimuth of −15° and an altitudeof +3° relative to reference line 220. In particular embodiments, anazimuth (which may be referred to as an azimuth angle) may represent ahorizontal angle with respect to reference line 220, and an altitude(which may be referred to as an altitude angle, elevation, or elevationangle) may represent a vertical angle with respect to reference line220.

In particular embodiments, a scan pattern 200 may include multiplepixels 210, and each pixel 210 may be associated with one or more laserpulses and one or more corresponding distance measurements. Inparticular embodiments, a cycle of scan pattern 200 may include a totalof P_(x)×P_(y) pixels 210 (e.g., a two-dimensional distribution of P_(x)by P_(y) pixels). As an example, scan pattern 200 may include adistribution with dimensions of approximately 100-2,000 pixels 210 alonga horizontal direction and approximately 4-400 pixels 210 along avertical direction. As another example, scan pattern 200 may include adistribution of 1,000 pixels 210 along the horizontal direction by 64pixels 210 along the vertical direction (e.g., the frame size is 1000×64pixels) for a total of 64,000 pixels per cycle of scan pattern 200. Inparticular embodiments, the number of pixels 210 along a horizontaldirection may be referred to as a horizontal resolution of scan pattern200, and the number of pixels 210 along a vertical direction may bereferred to as a vertical resolution. As an example, scan pattern 200may have a horizontal resolution of greater than or equal to 100 pixels210 and a vertical resolution of greater than or equal to 4 pixels 210.As another example, scan pattern 200 may have a horizontal resolution of100-2,000 pixels 210 and a vertical resolution of 4-400 pixels 210.

In particular embodiments, each pixel 210 may be associated with adistance (e.g., a distance to a portion of a target 130 from which anassociated laser pulse was scattered) or one or more angular values. Asan example, a pixel 210 may be associated with a distance value and twoangular values (e.g., an azimuth and altitude) that represent theangular location of the pixel 210 with respect to the lidar system 100.A distance to a portion of target 130 may be determined based at leastin part on a time-of-flight measurement for a corresponding pulse. Anangular value (e.g., an azimuth or altitude) may correspond to an angle(e.g., relative to reference line 220) of output beam 125 (e.g., when acorresponding pulse is emitted from lidar system 100) or an angle ofinput beam 135 (e.g., when an input signal is received by lidar system100). In particular embodiments, an angular value may be determinedbased at least in part on a position of a component of scanner 120. Asan example, an azimuth or altitude value associated with a pixel 210 maybe determined from an angular position of one or more correspondingscanning mirrors of scanner 120.

FIG. 3 illustrates an example lidar system 100 with an example overlapmirror 115. In particular embodiments, a lidar system 100 may include alight source 110 configured to emit pulses of light and a scanner 120configured to scan at least a portion of the emitted pulses of lightacross a field of regard. As an example, the light source 110 mayinclude a pulsed solid-state laser or a pulsed fiber laser, and theoptical pulses produced by the light source 110 may be directed throughaperture 310 of overlap mirror 115 and then coupled to scanner 120. Inparticular embodiments, a lidar system 100 may include a receiver 140configured to detect at least a portion of the scanned pulses of lightscattered by a target 130 located a distance D from the lidar system100. As an example, one or more pulses of light that are directeddownrange from lidar system 100 by scanner 120 (e.g., as part of outputbeam 125) may scatter off a target 130, and a portion of the scatteredlight may propagate back to the lidar system 100 (e.g., as part of inputbeam 135) and be detected by receiver 140.

In particular embodiments, lidar system 100 may include one or moreprocessors (e.g., a controller 150) configured to determine a distance Dfrom the lidar system 100 to a target 130 based at least in part on around-trip time of flight for an emitted pulse of light to travel fromthe lidar system 100 to the target 130 and back to the lidar system 100.The target 130 may be at least partially contained within a field ofregard of the lidar system 100 and located a distance D from the lidarsystem 100 that is less than or equal to a maximum range R_(MAX) of thelidar system 100. In particular embodiments, a maximum range (which maybe referred to as a maximum distance) of a lidar system 100 may refer tothe maximum distance over which the lidar system 100 is configured tosense or identify targets 130 that appear in a field of regard of thelidar system 100. The maximum range of lidar system 100 may be anysuitable distance, such as for example, 25 m, 50 m, 100 m, 200 m, 500 m,or 1 km. As an example, a lidar system 100 with a 200-m maximum rangemay be configured to sense or identify various targets 130 located up to200 m away from the lidar system 100. For a lidar system 100 with a200-m maximum range (R_(MAX)=200 m), the time of flight corresponding tothe maximum range is approximately 2·R_(MAX)/c≅1.33 μs.

In particular embodiments, light source 110, scanner 120, and receiver140 may be packaged together within a single housing, where a housingmay refer to a box, case, or enclosure that holds or contains all orpart of a lidar system 100. As an example, a lidar-system enclosure maycontain a light source 110, overlap mirror 115, scanner 120, andreceiver 140 of a lidar system 100. Additionally, the lidar-systemenclosure may include a controller 150. The lidar-system enclosure mayalso include one or more electrical connections for conveying electricalpower or electrical signals to or from the enclosure. In particularembodiments, one or more components of a lidar system 100 may be locatedremotely from a lidar-system enclosure. As an example, all or part oflight source 110 may be located remotely from a lidar-system enclosure,and pulses of light produced by the light source 110 may be conveyed tothe enclosure via optical fiber. As another example, all or part of acontroller 150 may be located remotely from a lidar-system enclosure.

In particular embodiments, light source 110 may include an eye-safelaser, or lidar system 100 may be classified as an eye-safe laser systemor laser product. An eye-safe laser, laser system, or laser product mayrefer to a system that includes a laser with an emission wavelength,average power, peak power, peak intensity, pulse energy, beam size, beamdivergence, exposure time, or scanned output beam such that emittedlight from the system presents little or no possibility of causingdamage to a person's eyes. As an example, light source 110 or lidarsystem 100 may be classified as a Class 1 laser product (as specified bythe 60825-1 standard of the International Electrotechnical Commission(IEC)) or a Class I laser product (as specified by Title 21, Section1040.10 of the United States Code of Federal Regulations (CFR)) that issafe under all conditions of normal use. In particular embodiments,lidar system 100 may be an eye-safe laser product (e.g., with a Class 1or Class I classification) configured to operate at any suitablewavelength between approximately 1400 nm and approximately 2100 nm. Asan example, lidar system 100 may include a laser with an operatingwavelength between approximately 1400 nm and approximately 1600 nm, andthe laser or the lidar system 100 may be operated in an eye-safe manner.As another example, lidar system 100 may be an eye-safe laser productthat includes a scanned laser with an operating wavelength betweenapproximately 1530 nm and approximately 1560 nm. As another example,lidar system 100 may be a Class 1 or Class I laser product that includesa fiber laser or solid-state laser with an operating wavelength betweenapproximately 1400 nm and approximately 1600 nm.

In particular embodiments, scanner 120 may include one or more mirrors,where each mirror is mechanically driven by a galvanometer scanner, aresonant scanner, a MEMS device, a voice coil motor, an electric motor,or any suitable combination thereof. A galvanometer scanner (which maybe referred to as a galvanometer actuator) may include agalvanometer-based scanning motor with a magnet and coil. When anelectrical current is supplied to the coil, a rotational force isapplied to the magnet, which causes a mirror attached to thegalvanometer scanner to rotate. The electrical current supplied to thecoil may be controlled to dynamically change the position of thegalvanometer mirror. A resonant scanner (which may be referred to as aresonant actuator) may include a spring-like mechanism driven by anactuator to produce a periodic oscillation at a substantially fixedfrequency (e.g., 1 kHz). A MEMS-based scanning device may include amirror with a diameter between approximately 1 and 10 mm, where themirror is rotated back and forth using electromagnetic or electrostaticactuation. A voice coil motor (which may be referred to as a voice coilactuator) may include a magnet and coil. When an electrical current issupplied to the coil, a translational force is applied to the magnet,which causes a mirror attached to the magnet to move or rotate. Anelectric motor, such as for example, a brushless DC motor or asynchronous electric motor, may be used to continuously rotate a mirrorat a substantially fixed frequency (e.g., a rotational frequency ofapproximately 1 Hz, 10 Hz, 50 Hz, 100 Hz, 500 Hz, or 1,000 Hz). Themirror may be continuously rotated in one rotation direction (e.g.,clockwise or counter-clockwise relative to a particular rotation axis).

In particular embodiments, a scanner 120 may include any suitable numberof mirrors driven by any suitable number of mechanical actuators. As anexample, a scanner 120 may include a single mirror configured to scan anoutput beam 125 along a single direction (e.g., a scanner 120 may be aone-dimensional scanner that scans along a horizontal or verticaldirection). The mirror may be driven by one actuator (e.g., agalvanometer) or two actuators configured to drive the mirror in apush-pull configuration. As another example, a scanner 120 may include asingle mirror that scans an output beam 125 along two directions (e.g.,horizontal and vertical). The mirror may be driven by two actuators,where each actuator provides rotational motion along a particulardirection or about a particular axis. As another example, a scanner 120may include two mirrors, where one mirror scans an output beam 125 alonga substantially horizontal direction and the other mirror scans theoutput beam 125 along a substantially vertical direction. In the exampleof FIG. 3, scanner 120 includes two mirrors, mirror 300-1 and mirror300-2. Mirror 300-2 rotates along the Θ_(y) direction and scans outputbeam 125 along a substantially vertical direction, and mirror 300-1rotates along the Θ_(x) direction and scans output beam 125 along asubstantially horizontal direction.

In particular embodiments, a scanner 120 may include two mirrors, whereeach mirror is driven by a corresponding galvanometer scanner. As anexample, scanner 120 may include a galvanometer actuator that scansmirror 300-1 along a first direction (e.g., horizontal), and scanner 120may include another galvanometer actuator that scans mirror 300-2 alonga second direction (e.g., vertical). In particular embodiments, ascanner 120 may include two mirrors, where one mirror is driven by agalvanometer actuator and the other mirror is driven by a resonantactuator. As an example, a galvanometer actuator may scan mirror 300-1along a first direction, and a resonant actuator may scan mirror 300-2along a second direction. The first and second scanning directions maybe substantially orthogonal to one another. As an example, the firstdirection may be substantially vertical, and the second direction may besubstantially horizontal, or vice versa. In particular embodiments, ascanner 120 may include two mirrors, where one mirror is driven by anelectric motor and the other mirror is driven by a galvanometeractuator. As an example, mirror 300-1 may be a polygon mirror that isrotated about a fixed axis by an electric motor (e.g., a brushless DCmotor), and mirror 300-2 may be driven by a galvanometer or MEMSactuator. In particular embodiments, a scanner 120 may include twomirrors, where both mirrors are driven by electric motors. As anexample, mirror 300-2 may be a polygon mirror driven by an electricmotor, and mirror 300-1 may be driven by another electric motor. Inparticular embodiments, a scanner 120 may include one mirror driven bytwo actuators which are configured to scan the mirror along twosubstantially orthogonal directions. As an example, one mirror may bedriven along a substantially horizontal direction by a resonant actuatoror a galvanometer actuator, and the mirror may also be driven along asubstantially vertical direction by a galvanometer actuator. As anotherexample, a mirror may be driven along two substantially orthogonaldirections by two resonant actuators or by two electric motors.

In particular embodiments, a scanner 120 may include a mirror configuredto be scanned along one direction by two actuators arranged in apush-pull configuration. Driving a mirror in a push-pull configurationmay refer to a mirror that is driven in one direction by two actuators.The two actuators may be located at opposite ends or sides of themirror, and the actuators may be driven in a cooperative manner so thatwhen one actuator pushes on the mirror, the other actuator pulls on themirror, and vice versa. As an example, a mirror may be driven along ahorizontal or vertical direction by two voice coil actuators arranged ina push-pull configuration. In particular embodiments, a scanner 120 mayinclude one mirror configured to be scanned along two axes, where motionalong each axis is provided by two actuators arranged in a push-pullconfiguration. As an example, a mirror may be driven along a horizontaldirection by two resonant actuators arranged in a horizontal push-pullconfiguration, and the mirror may be driven along a vertical directionby another two resonant actuators arranged in a vertical push-pullconfiguration.

In particular embodiments, a scanner 120 may include two mirrors whichare driven synchronously so that the output beam 125 is directed alongany suitable scan pattern 200. As an example, a galvanometer actuatormay drive mirror 300-1 with a substantially linear back-and-forth motion(e.g., the galvanometer may be driven with a substantially sinusoidal ortriangle-shaped waveform) that causes output beam 125 to trace asubstantially horizontal back-and-forth pattern. Additionally, anothergalvanometer actuator may scan mirror 300-2 along a substantiallyvertical direction. For example, the two galvanometers may besynchronized so that for every 64 horizontal traces, the output beam 125makes a single trace along a vertical direction. As another example, aresonant actuator may drive mirror 300-1 along a substantiallyhorizontal direction, and a galvanometer actuator or a resonant actuatormay scan mirror 300-2 along a substantially vertical direction.

In particular embodiments, a scanner 120 may include one mirror drivenby two or more actuators, where the actuators are driven synchronouslyso that the output beam 125 is directed along a particular scan pattern200. As an example, one mirror may be driven synchronously along twosubstantially orthogonal directions so that the output beam 125 followsa scan pattern 200 that includes substantially straight lines. Inparticular embodiments, a scanner 120 may include two mirrors drivensynchronously so that the synchronously driven mirrors trace out a scanpattern 200 that includes substantially straight lines. As an example,the scan pattern 200 may include a series of substantially straightlines directed substantially horizontally, vertically, or along anyother suitable direction. The straight lines may be achieved by applyinga dynamically adjusted deflection along a vertical direction (e.g., witha galvanometer actuator) as an output beam 125 is scanned along asubstantially horizontal direction (e.g., with a galvanometer orresonant actuator). If a vertical deflection is not applied, the outputbeam 125 may trace out a curved path as it scans from side to side. Byapplying a vertical deflection as the mirror is scanned horizontally, ascan pattern 200 that includes substantially straight lines may beachieved. In particular embodiments, a vertical actuator may be used toapply both a dynamically adjusted vertical deflection as the output beam125 is scanned horizontally as well as a discrete vertical offsetbetween each horizontal scan (e.g., to step the output beam 125 to asubsequent row of a scan pattern 200).

In the example of FIG. 3, lidar system 100 produces an output beam 125and receives light from an input beam 135. The output beam 125, whichincludes at least a portion of the pulses of light emitted by lightsource 110, may be scanned across a field of regard. The input beam 135may include at least a portion of the scanned pulses of light which arescattered by one or more targets 130 and detected by receiver 140. Inparticular embodiments, output beam 125 and input beam 135 may besubstantially coaxial. The input and output beams being substantiallycoaxial may refer to the beams being at least partially overlapped orsharing a common propagation axis so that input beam 135 and output beam125 travel along substantially the same optical path (albeit in oppositedirections). As output beam 125 is scanned across a field of regard, theinput beam 135 may follow along with the output beam 125 so that thecoaxial relationship between the two beams is maintained.

In particular embodiments, a lidar system 100 may include an overlapmirror 115 configured to overlap the input beam 135 and output beam 125so that they are substantially coaxial. In FIG. 3, the overlap mirror115 includes a hole, slot, or aperture 310 which the output beam 125passes through and a reflecting surface 320 that reflects at least aportion of the input beam 135 toward the receiver 140. The overlapmirror 115 may be oriented so that input beam 135 and output beam 125are at least partially overlapped. In particular embodiments, input beam135 may pass through a lens 330 which focuses the beam onto an activeregion of the receiver 140. The active region may refer to an area overwhich receiver 140 may receive or detect input light. The active regionmay have any suitable size or diameter d, such as for example, adiameter of approximately 25 μm, 50 μm, 80 μm, 100 μm, 200 μm, 500 μm, 1mm, 2 mm, or 5 mm. In particular embodiments, overlap mirror 115 mayhave a reflecting surface 320 that is substantially flat or thereflecting surface 320 may be curved (e.g., mirror 115 may be anoff-axis parabolic mirror configured to focus the input beam 135 onto anactive region of the receiver 140). A reflecting surface 320 (which maybe referred to as a reflective surface 320) may include a reflectivemetallic coating (e.g., gold, silver, or aluminum) or a reflectivedielectric coating, and the reflecting surface 320 may have any suitablereflectivity R at an operating wavelength of the light source 110 (e.g.,R greater than or equal to 70%, 80%, 90%, 95%, 98%, or 99%).

In particular embodiments, aperture 310 may have any suitable size ordiameter Φ₁, and input beam 135 may have any suitable size or diameterΦ₂, where Φ₂ is greater than Φ₁. As an example, aperture 310 may have adiameter Φ₁ of approximately 0.2 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, 5 mm, or10 mm, and input beam 135 may have a diameter Φ₂ of approximately 2 mm,5 mm, 10 mm, 15 mm, 20 mm, 30 mm, 40 mm, or 50 mm. In particularembodiments, reflective surface 320 of overlap mirror 115 may reflectgreater than or equal to 70% of input beam 135 toward the receiver 140.As an example, if reflective surface 320 has a reflectivity R at anoperating wavelength of the light source 110, then the fraction of inputbeam 135 directed toward the receiver 140 may be expressed asR×[1−(Φ₁/Φ₂)²]. For example, if R is 95%, Φ₁ is 2 mm, and Φ₂ is 10 mm,then approximately 91% of input beam 135 may be directed toward thereceiver 140 by reflective surface 320.

FIG. 4 illustrates an example lidar system 100 with an example rotatingpolygon mirror 300-1. In particular embodiments, a scanner 120 mayinclude a polygon mirror 300-1 configured to scan output beam 125 alonga particular direction. In the example of FIG. 4, scanner 120 includestwo scanning mirrors: (1) a polygon mirror 300-1 that rotates along theΘ_(x) direction and (2) a scanning mirror 300-2 that oscillates back andforth along the Θ_(y) direction. The output beam 125 from light source110, which passes alongside mirror 115, is reflected by a reflectingsurface (e.g., surface 320A, 320B, 320C, or 320D) of polygon mirror300-1 and is then reflected by reflecting surface 320 of mirror 300-2.Scattered light from a target 130 returns to the lidar system 100 asinput beam 135. The input beam 135 reflects from mirror 300-2, polygonmirror 300-1, and mirror 115, which directs input beam 135 throughfocusing lens 330 and to receiver 140.

In particular embodiments, a polygon mirror 300-1 may be configured torotate along a Θ_(x) or Θ_(y) direction and scan output beam 125 along asubstantially horizontal or vertical direction, respectively. A rotationalong a Θ_(x) direction may refer to a rotational motion of mirror 300-1that results in output beam 125 scanning along a substantiallyhorizontal direction. Similarly, a rotation along a Θ_(y) direction mayrefer to a rotational motion that results in output beam 125 scanningalong a substantially vertical direction. In FIG. 4, mirror 300-1 is apolygon mirror that rotates along the Θ_(x) direction and scans outputbeam 125 along a substantially horizontal direction, and mirror 300-2rotates along the Θ_(y) direction and scans output beam 125 along asubstantially vertical direction. In particular embodiments, a polygonmirror 300-1 may be configured to scan output beam 125 along anysuitable direction. As an example, a polygon mirror 300-1 may scanoutput beam 125 at any suitable angle with respect to a horizontal orvertical direction, such as for example, at an angle of approximately0°, 10°, 20°, 30°, 45°, 60°, 70°, 80°, or 90° with respect to ahorizontal or vertical direction.

In particular embodiments, a polygon mirror 300-1 may refer to amulti-sided object having reflective surfaces 320 on two or more of itssides or faces. As an example, a polygon mirror may include any suitablenumber of reflective faces (e.g., 2, 3, 4, 5, 6, 7, 8, or 10 faces),where each face includes a reflective surface 320. A polygon mirror300-1 may have a cross-sectional shape of any suitable polygon, such asfor example, a triangle (with three reflecting surfaces 320), square(with four reflecting surfaces 320), pentagon (with five reflectingsurfaces 320), hexagon (with six reflecting surfaces 320), heptagon(with seven reflecting surfaces 320), or octagon (with eight reflectingsurfaces 320). In FIG. 4, the polygon mirror 300-1 has a substantiallysquare cross-sectional shape and four reflecting surfaces (320A, 320B,320C, and 320D). The polygon mirror 300-1 in FIG. 4 may be referred toas a square mirror, a cube mirror, or a four-sided polygon mirror. InFIG. 4, the polygon mirror 300-1 may have a shape similar to a cube,cuboid, or rectangular prism. Additionally, the polygon mirror 300-1 mayhave a total of six sides, where four of the sides are faces withreflective surfaces (320A, 320B, 320C, and 320D).

In particular embodiments, a polygon mirror 300-1 may be continuouslyrotated in a clockwise or counter-clockwise rotation direction about arotation axis of the polygon mirror 300-1. The rotation axis maycorrespond to a line that is perpendicular to the plane of rotation ofthe polygon mirror 300-1 and that passes through the center of mass ofthe polygon mirror 300-1. In FIG. 4, the polygon mirror 300-1 rotates inthe plane of the drawing, and the rotation axis of the polygon mirror300-1 is perpendicular to the plane of the drawing. An electric motormay be configured to rotate a polygon mirror 300-1 at a substantiallyfixed frequency (e.g., a rotational frequency of approximately 1 Hz (or1 revolution per second), 10 Hz, 50 Hz, 100 Hz, 500 Hz, or 1,000 Hz). Asan example, a polygon mirror 300-1 may be mechanically coupled to anelectric motor (e.g., a brushless DC motor or a synchronous electricmotor) which is configured to spin the polygon mirror 300-1 at arotational speed of approximately 160 Hz (or, 9600 revolutions perminute (RPM)).

In particular embodiments, output beam 125 may be reflected sequentiallyfrom the reflective surfaces (320A, 320B, 320C, and 320D) as the polygonmirror 300-1 is rotated. This results in the output beam 125 beingscanned along a particular scan axis (e.g., a horizontal or verticalscan axis) to produce a sequence of scan lines, where each scan linecorresponds to a reflection of the output beam 125 from one of thereflective surfaces of the polygon mirror 300-1. In FIG. 4, the outputbeam 125 reflects off of reflective surface 320A to produce one scanline. Then, as the polygon mirror 300-1 rotates, the output beam 125reflects off of reflective surfaces 320B, 320C, and 320D to produce asecond, third, and fourth respective scan line.

In particular embodiments, output beam 125 may be directed to pass by aside of mirror 115 rather than passing through mirror 115. As anexample, mirror 115 may not include an aperture 310, and the output beam125 may be directed to pass along a side of mirror 115. In the exampleof FIG. 3, lidar system includes an overlap mirror 115 with an aperture310 that output beam 125 passes through. In the example of FIG. 4,output beam 125 from light source 110 is directed to pass by mirror 115(which does not include an aperture 310) and then to polygon mirror300-1.

FIG. 5 illustrates an example light-source field of view (FOV_(L)) andreceiver field of view (FOV_(R)) for a lidar system 100. A light source110 of lidar system 100 may emit pulses of light as the FOV_(L) andFOV_(R) are scanned by scanner 120 across a field of regard (FOR). Inparticular embodiments, a light-source field of view may refer to anangular cone illuminated by the light source 110 at a particular instantof time. Similarly, a receiver field of view may refer to an angularcone over which the receiver 140 may receive or detect light at aparticular instant of time, and any light outside the receiver field ofview may not be received or detected. As an example, as the light-sourcefield of view is scanned across a field of regard, a portion of a pulseof light emitted by the light source 110 may be sent downrange fromlidar system 100, and the pulse of light may be sent in the directionthat the FOV_(L) is pointing at the time the pulse is emitted. The pulseof light may scatter off a target 130, and the receiver 140 may receiveand detect a portion of the scattered light that is directed along orcontained within the FOV_(R).

In particular embodiments, scanner 120 may be configured to scan both alight-source field of view and a receiver field of view across a fieldof regard of the lidar system 100. Multiple pulses of light may beemitted and detected as the scanner 120 scans the FOV_(L) and FOV_(R)across the field of regard of the lidar system 100 while tracing out ascan pattern 200. In particular embodiments, the light-source field ofview and the receiver field of view may be scanned synchronously withrespect to one another, so that as the FOV_(L) is scanned across a scanpattern 200, the FOV_(R) follows substantially the same path at the samescanning speed. Additionally, the FOV_(L) and FOV_(R) may maintain thesame relative position to one another as they are scanned across thefield of regard. As an example, the FOV_(L) may be substantiallyoverlapped with or centered inside the FOV_(R) (as illustrated in FIG.5), and this relative positioning between FOV_(L) and FOV_(R) may bemaintained throughout a scan. As another example, the FOV_(R) may lagbehind the FOV_(L) by a particular, fixed amount throughout a scan(e.g., the FOV_(R) may be offset from the FOV_(L) in a directionopposite the scan direction).

In particular embodiments, the FOV_(L) may have an angular size orextent Θ_(L) that is substantially the same as or that corresponds tothe divergence of the output beam 125, and the FOV_(R) may have anangular size or extent Θ_(R) that corresponds to an angle over which thereceiver 140 may receive and detect light. In particular embodiments,the receiver field of view may be any suitable size relative to thelight-source field of view. As an example, the receiver field of viewmay be smaller than, substantially the same size as, or larger than theangular extent of the light-source field of view. In particularembodiments, the light-source field of view may have an angular extentof less than or equal to 50 milliradians, and the receiver field of viewmay have an angular extent of less than or equal to 50 milliradians. TheFOV_(L) may have any suitable angular extent Θ_(L), such as for example,approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2 mrad, 3mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. Similarly, theFOV_(R) may have any suitable angular extent Θ_(R), such as for example,approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2 mrad, 3mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. In particularembodiments, the light-source field of view and the receiver field ofview may have approximately equal angular extents. As an example, Θ_(L)and Θ_(R) may both be approximately equal to 1 mrad, 2 mrad, or 4 mrad.In particular embodiments, the receiver field of view may be larger thanthe light-source field of view, or the light-source field of view may belarger than the receiver field of view. As an example, Θ_(L) may beapproximately equal to 3 mrad, and Θ_(R) may be approximately equal to 4mrad. As another example, Θ_(R) may be approximately L times larger thanΘ_(L), where L is any suitable factor, such as for example, 1.1, 1.2,1.5, 2, 3, 5, or 10.

In particular embodiments, a pixel 210 may represent or may correspondto a light-source field of view or a receiver field of view. As theoutput beam 125 propagates from the light source 110, the diameter ofthe output beam 125 (as well as the size of the corresponding pixel 210)may increase according to the beam divergence Θ_(L). As an example, ifthe output beam 125 has a Θ_(L) of 2 mrad, then at a distance of 100 mfrom the lidar system 100, the output beam 125 may have a size ordiameter of approximately 20 cm, and a corresponding pixel 210 may alsohave a corresponding size or diameter of approximately 20 cm. At adistance of 200 m from the lidar system 100, the output beam 125 and thecorresponding pixel 210 may each have a diameter of approximately 40 cm.

FIG. 6 illustrates an example scan pattern 200 that includes multiplescan lines 410 and multiple pixels 210. In particular embodiments, scanpattern 200 may include any suitable number of scan lines 410 (e.g.,approximately 1, 2, 5, 10, 20, 50, 100, 500, or 1,000 scan lines 410),and each scan line 410 of a scan pattern 200 may include any suitablenumber of pixels (e.g., 1, 2, 5, 10, 20, 50, 100, 200, 500, 1,000,2,000, or 5,000 pixels 210). The scan pattern 200 illustrated in FIG. 6includes approximately nine scan lines 410, and each scan line 410includes approximately 18 pixels 210. In particular embodiments, eachscan line 410 of a scan pattern 200 may include approximately the samenumber of pixels 210. As an example, each scan line 410 of a scanpattern 200 may include between approximately 950 and approximately1,050 pixels 210. In particular embodiments, a scan pattern 200 wherethe scan lines 410 are scanned in two directions may be referred to as abidirectional scan pattern 200, and a scan pattern 200 where the scanlines 410 are scanned in the same direction may be referred to as aunidirectional scan pattern 200. The scan pattern 200 in FIG. 6 may bereferred to as a bidirectional scan pattern 200 where the scan lines 410alternate between scanning from right to left and scanning from left toright. A bidirectional scan pattern 200 may be produced by a scanner 120that includes a scanning mirror that oscillates in a back-and-forthmotion corresponding to the bidirectional scan pattern 200.

In particular embodiments, a scan pattern 200 may include a retrace 405where a scanner 120 resets from an end point of a scan 200 back to astarting point of the scan 200. The scan pattern 200 illustrated in FIG.6 starts at the upper-left portion of the FOR and ends at thelower-right portion. In FIG. 6, the scan pattern 200 includes retrace405 represented by a dashed diagonal line that connects the end of scanpattern 200 to the beginning. In particular embodiments, lidar system100 may not send out pulses or acquire distance data during a retrace405, or lidar system 100 may acquire distance data during a retrace 405(e.g., a retrace path may include one or more pixels 210).

In particular embodiments, the pixels 210 of a scan pattern 200 may besubstantially evenly spaced with respect to time or angle. As anexample, each pixel 210 (and its associated pulse) may be separated froman immediately preceding or following pixel 210 by any suitable timeinterval, such as for example a time interval of approximately 0.5 μs,1.0 μs, 1.4 μs, or 2.0 μs. In FIG. 6, pixels 210A, 210B, and 210C may beassociated with pulses that were emitted with a 1.6 μs fixed timeinterval between the pulses. As another example, each pixel 210 (and itsassociated pulse) may be separated from an immediately preceding orfollowing pixel 210 by any suitable angle, such as for example an angleof approximately 0.01°, 0.02°, 0.05°, 0.1°, 0.2°, 0.3°, 0.5°, or 1°. InFIG. 6, pixels 210A and 210B may have an angular separation ofapproximately 0.1° (e.g., pixels 210A and 210B may each be associatedwith optical beams separated by an angle of 0.1°). In particularembodiments, the pixels 210 of a scan pattern 200 may have an adjustablespacing with respect to time or angle. As an example, a time interval orangle separating two successive pixels 210 may be dynamically variedduring a scan or from one scan to a subsequent scan.

In particular embodiments, lidar system 100 may include a scanner 120configured to direct output beam 125 along any suitable scan pattern200. As an example, all or part of scan pattern 200 may follow asubstantially sinusoidal path, triangle-wave path, square-wave path,sawtooth path, piecewise linear path, periodic-function path, or anyother suitable path or combination of paths. In the example of FIG. 6,scan pattern 200 corresponds to an approximately sinusoidal path, wherepixels 210 are arranged along a sinusoidal curve.

In particular embodiments, pixels 210 may be substantially evenlydistributed across scan pattern 200, or pixels 210 may have adistribution or density that varies across a FOR of scan pattern 200. Inthe example of FIG. 6, pixels 210 have a greater density toward the leftand right edges of the FOR, and the pixel density in the middle regionof the FOR is lower compared to the edges. As an example, pixels 210 maybe distributed so that ≥40% of the pixels 210 are located in the left25% of the FOR, ≥40% of the pixels 210 are located in the right 25% ofthe FOR, and the remaining <20% of the pixels 210 are located in themiddle 50% of the FOR. In particular embodiments, a time interval orangle between pixels 210 may be dynamically adjusted during a scan sothat a scan pattern 200 has a particular distribution of pixels 210(e.g., a higher density of pixels 210 in one or more particularregions). As an example, a scan pattern 200 may be configured to have ahigher density of pixels 210 in a middle or central region of scan 200or toward one or more edges of scan 200 (e.g., a middle region or aleft, right, upper, or lower edge that includes approximately 5%, 10%,20%, 30%, or any other suitable percentage of the FOR of scan pattern200). For example, pixels 210 may be distributed so that ≥50% of thepixels 210 are located in a central, left, or right region of scanpattern 200 with the remaining <50% of the pixels 210 distributedthroughout the rest of scan pattern 200. As another example, a scanpattern 200 may have a higher density of pixels along a right edge ofthe scan pattern 200 than along a left edge of the scan pattern 200.

In particular embodiments, a distribution of pixels 210 in a scanpattern 200 may be determined, at least in part, by a pulse period oflight source 110, a scanning speed provided by scanner 120, or a shapeor path followed by scan pattern 200. As an example, the pulse period oflight source 110 may be a substantially fixed value, or the pulse periodmay be adjusted dynamically during a scan to vary the density of pixels210 across the scan region. As another example, an angular speed withwhich a mirror (e.g., mirror 300-1 or mirror 300-2) of scanner 120rotates may be substantially fixed or may vary during a scan. As anotherexample, a scan pattern 200 may provide for a varying distribution ofpixels 210 based on a shape of the pattern. For example, a triangle-wavescan pattern 200 (combined with a substantially constant pulse periodand angular speed) may provide a substantially uniform distribution ofpixels 210 along the horizontal direction, while a sinusoidal scanpattern 200 may result in a higher density of pixels 210 along the leftand right edges and a lower density of pixels 210 in the middle region.Additionally, two or more scan parameters may be selected or adjusted tooptimize or adjust the density of pixels 210 in a scan pattern 200. Asan example, a sinusoidal scan pattern 200 may be combined with adynamically adjusted pulse period of light source 100 to provide for ahigher density of pixels 210 along the right edge and a lower density ofpixels 210 in the middle region and along the left edge.

In particular embodiments, a particular scan pattern 200 may be repeatedfrom one scan to the next, or one or more parameters of a scan pattern200 may be adjusted or varied within a scan or from one scan to another.As an example, a time interval or angle between pixels 210 may be variedfrom one scan to another scan. A relatively long time interval may beapplied in an initial scan to produce a moderate-density point cloud,and a relatively short time interval may be applied in a subsequent scanto produce a high-density point cloud. As another example, a timeinterval or angle between pixels 210 may be varied within a particularscan pattern 200. For a particular region of a scan pattern 200, a timeinterval may be decreased to produce a higher density of pixels 210within that particular region.

FIG. 7 illustrates an example unidirectional scan pattern 200. Each scanline 410 in FIG. 7 travels across the FOR in substantially the samedirection (e.g., from left to right). In particular embodiments, scanlines 410 of a unidirectional scan pattern 200 may be directed across aFOR in any suitable direction, such as for example, from left to right,from right to left, from top to bottom, from bottom to top, or at anysuitable angle (e.g., at a 5°, 10°, 30°, or 45° angle) with respect to ahorizontal or vertical axis. In particular embodiments, each scan line410 in a unidirectional scan pattern 200 may be a separate line that isnot directly connected to a previous or subsequent scan line 410.

In particular embodiments, a unidirectional scan pattern 200 may beproduced by a scanner 120 that includes a polygon mirror (e.g., polygonmirror 300-1 of FIG. 4), where each scan line 410 is associated with aparticular reflective surface 320 of the polygon mirror. As an example,reflective surface 320A of polygon mirror 300-1 in FIG. 4 may producescan line 410A in FIG. 7. Similarly, as the polygon mirror 300-1rotates, reflective surfaces 320B, 320C, and 320D may successivelyproduce scan lines 410B, 410C, and 410D, respectively. Additionally, fora subsequent revolution of the polygon mirror 300-1, the scan lines410A′, 410B′, 410C′, and 410D′ may be successively produced byreflections of the output beam 125 from reflective surfaces 320A, 320B,320C, and 320D, respectively. In particular embodiments, N successivescan lines 410 of a unidirectional scan pattern 200 may correspond toone full revolution of a N-sided polygon mirror. As an example, the fourscan lines 410A, 410B, 410C, and 410D in FIG. 7 may correspond to onefull revolution of the four-sided polygon mirror 300-1 in FIG. 4.Additionally, a subsequent revolution of the polygon mirror 300-1 mayproduce the next four scan lines 410A′, 410B′, 410C′, and 410D′ in FIG.7.

In particular embodiments, during at least a portion of a scan, lightsource 110 may be configured to emit pulses of light at a substantiallyconstant pulse repetition frequency, or light source 110 may beconfigured to vary the pulse repetition frequency. Additionally, ascanning mirror of scanner 120 may scan output beam 125 (which includesat least a portion of the pulses of light emitted by the light source110) at a substantially constant angular scanning speed. As an example,polygon mirror 300-1 in FIG. 4 may rotate at a substantially constantrotation speed, and the output beam 125 may scan across the FOR (e.g.,along scan axis Θ_(x)) at a corresponding constant angular scanningspeed. If a polygon mirror 300-1 has a rotation speed of R (e.g., inunits of revolutions per second or degrees per second), then the outputbeam 125 may scan across the FOR at an angular scanning speed ofapproximately 2R, since a Θ-degree rotation of polygon mirror 300-1results in a 2Θ-degree angular motion of output beam 125. For example,if the polygon mirror 300-1 has a rotation speed of 10,000 degrees persecond, then the output beam 125 may scan across the FOR at an angularscanning speed of approximately 20,000 degrees per second. In particularembodiments, the number of scan lines 410 per second produced by apolygon mirror 300-1 with N reflective surfaces 320 and a rotation speedR may be expressed as R×N, where R has units of revolutions per second.As an example, if the 4-sided polygon mirror 300-1 in FIG. 4 has arotation speed of 150 revolutions per second, then the lidar system 100may produce approximately 600 scan lines 410 per second.

In particular embodiments, the angular scanning speed ω_(x) (in units ofdeg/s) of the output beam 125 along scan axis Θ_(x) may be expressed asω_(x)=2×R×360, where R has units of revolutions per second. For example,if polygon mirror 300-1 rotates at 100 revolutions per second (whichcorresponds to an angular rotation rate of approximately 36,000 degreesper second, or 628 radians per second), then the output beam 125 mayscan along scan axis Θ_(x) at an angular scanning speed of approximately72,000 degrees per second (or approximately 1,257 radians per second).The expression FOR_(H)/(2×R×360) represents the time for the output beam125 to make a single scan across FOR_(H) (along scan axis Θ_(x)) andproduce a single scan line 410. As an example, for a FOR_(H) of 60° anda 100-Hz rotation speed (100 revolutions per second), one scan line 410may be traced across the FOR_(H) in approximately 0.83 ms. In particularembodiments, each scan line 410 of a scan pattern 200 may includeapproximately the same number of pixels 210. As an example, if thelight-source pulse repetition frequency (PRF) is substantially constantand the rotation speed R of polygon mirror 300-1 is substantiallyconstant, then each scan line 410 may include approximately the samenumber of pixels 210. As another example, each of the scan lines 410 inFIG. 7 may include approximately 1,000 pixels 210. The approximatenumber of pixels 210 in one scan line 410 may be found from theexpression P=(PRF×FOR_(H))/(2×R×360). For example, if the rotation speedR is 100 revolutions per second, the FOR_(H) is 60° degrees, and the PRFis 600 kHz, then each scan line 410 includes approximately P=500 pixels210.

In particular embodiments, the output beam 125 may have any suitableangular scan rate along the Θ_(y) scan axis, such as for example anangular scan rate of approximately 1, 2, 5, 10, 20, 50, 100, 300, or1,000 degrees per second. In particular embodiments, an angular scanrate may be referred to as a scan rate, a scan speed, an angular scanspeed, a scanning speed, or an angular scanning speed. The angularscanning speed along scan axis Θ_(y) may be expressed asω_(y)=ΔΘ_(y)/τ_(y), where ΔΘ_(y) is an angular range of the scan pattern200 along the Θ_(y) scan axis, and τ_(y) is a time for the output beam125 to travel across ΔΘ_(y) and trace out a single scan pattern 200 froma starting point to an end point (not including the time to perform aretrace 405). As an example, if ΔΘ_(y) is 30° and τ_(y) is 100 ms, thenthe angular scanning speed along scan axis Θ_(y) is approximately 300degrees per second. As another example, if ΔΘ_(y) is 2° and τ_(y) is 40ms, then the angular scanning speed along scan axis Θ_(y) isapproximately 50 degrees per second. In FIG. 7, the angular scan rangealong the Θ_(y) scan axis is approximately equal to FOR_(V). The scantime τ_(y) may be related to the frame rate F at which the lidar system100 scans by the expression F=1/(τ_(y)+τ_(retrace)), where τ_(retrace)is a time for the output beam 125 to traverse the retrace path 405.Based on this, the angular scanning speed along scan axis Θ_(y) may beexpressed as ω_(y)=(ΔΘ_(y)×F)/(1−F×τ_(retrace)). As an example, for a10-Hz frame rate over a 30° range with a 10 ms retrace time, thescanning speed ω_(y) is approximately 333 degrees per second. As anotherexample, for a 1-Hz scan rate over a 5° range with a 20 ms retrace time,the scanning speed ω_(y) is approximately 5.1 degrees per second.

In particular embodiments, a scan line 410 may have an incline angle δwith respect to the Θ_(x) axis. The incline angle δ may have anysuitable value, such as for example, approximately 0°, 0.1°, 0.2°, 0.5°,1°, 2°, 5°, or 10°. The incline angle δ may be oriented upward ordownward according to the direction the output beam 125 is scanned alongthe Θ_(y) scan axis. In FIG. 7, the output beam is scanned along theΘ_(y) scan axis from top to bottom, and each scan line 410 is angleddownward (with respect to the Θ_(x) axis) at an incline angle δ ofapproximately 4°. In particular embodiments, the incline angle δ maydepend on the angular scanning speeds along the scan axes Θ_(x) andΘ_(y) and may be expressed as δ=arctan(ω_(y)/ω_(x)). As an example, ifthe output beam 125 is scanned along scan axis Θ_(x) at an angularscanning speed ω_(x) of 72,000 degrees per second and along scan axisΘ_(y) at an angular scanning speed ω_(y) of 300 degrees per second, thenscan lines 410 may have an incline angle δ of approximately 4.2 mrad(or, approximately 0.24°). As another example, if ω_(x) is 10,000degrees per second and ω_(y) is 350 degrees per second, then scan lines410 may have an incline angle δ of approximately 2°, and each scan line410 may be oriented downward at 2° with respect to the Θ_(x) axis.

FIG. 8 illustrates an example seed laser 400 that includes a laser diode440 driven by a pulse generator 430. In particular embodiments, a seedlaser 400 may include a function generator 420, a pulse generator 430, alaser diode 440, or a temperature controller 450. In the example of FIG.8, seed laser 400 includes function generator 420 coupled to pulsegenerator 430, which is in turn coupled to laser diode 440.Additionally, temperature controller 450 is coupled to laser diode 440.In particular embodiments, all or part of function generator 420, pulsegenerator 430, or temperature controller 450 may be included in seedlaser 400 or may be located remote from seed laser 400. As an example,all or part of function generator 420, pulse generator 430, ortemperature controller 450 may be included in controller 150. Inparticular embodiments, a seed laser 400 or a laser diode 440 may bereferred to as a pulsed laser, a pulsed laser diode, a seed laser diode,a seed laser, or a seed.

In particular embodiments, seed laser 400 may produce optical seedpulses, which are emitted at the seed-laser output (which may be afree-space output or a fiber-optic output). In particular embodiments,the optical seed pulses may have a pulse repetition frequency of lessthan or equal to 100 MHz (e.g., approximately 500 kHz, 640 kHz, 750 kHz,1 MHz, 2 MHz, 4 MHz, 5 MHz, 10 MHz, 20 MHz, 50 MHz, or 100 MHz), a pulseduration of less than or equal to 100 nanoseconds (e.g., approximately200 ps, 400 ps, 500 ps, 800 ps, 1 ns, 2 ns, 4 ns, 8 ns, 10 ns, 20 ns, 50ns, or 100 ns), a duty cycle of less than or equal to 10% (e.g.,approximately 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.5%, 1%, 2%, 5%, or10%), or an operating wavelength of between 1400 nm and 2050 nm. As anexample, the seed pulses may have a pulse repetition frequency of500-750 kHz, a pulse duration of less than or equal to 2 ns, and a dutycycle of less than or equal to 0.1%. As another example, the seed pulsesmay have a pulse repetition frequency of approximately 640 kHz and apulse duration of approximately 1 ns (which corresponds to a duty cycleof approximately 0.064%). As another example, the seed pulses may have apulse repetition frequency of approximately 750 kHz and a pulse durationof approximately 20 ns (which corresponds to a duty cycle ofapproximately 1.5%). A duty cycle may be determined from the ratio ofpulse duration to pulse period or from the product of pulse duration andpulse repetition frequency. The laser diode 440 may have any suitableoperating wavelength, such as for example, an operating wavelength ofapproximately 1400 nm, 1500 nm, 1550 nm, 1600 nm, or 2000 nm. Inparticular embodiments, the seed pulses may be relatively low-poweroptical pulses, and the seed-laser output may be coupled to one or moreoptical amplifiers configured to amplify the low-power pulses to produceamplified pulses of light which are emitted by light source 110. As anexample, the seed pulses may have an average power of greater than orequal to 1 μW. As another example, the seed pulses may have an averagepower of between approximately 0.1 μW and 10 μW.

In particular embodiments, seed laser 400 may include a laser diode 440that is electrically driven by pulse generator 430 to produce opticalseed pulses. In the example of FIG. 8, function generator 420 supplies avoltage signal 422 to pulse generator 430, and pulse generator 430drives laser diode 440 with a current signal 432. As an example,function generator 420 may produce a pulsed voltage signal with a pulserepetition frequency of between approximately 0.5 and 2 MHz and a pulseduration of approximately 1-2 ns. Pulse generator 430 may drive laserdiode 440 with a pulsed current signal 432 that corresponds to thevoltage signal 422 received from function generator 420. In particularembodiments, voltage signal 422 may include voltage pulses having anysuitable shape, such as for example, square-shaped pulses,triangle-shaped pulses, Gaussian-shaped pulses, or pulses having anarbitrary shape or a combination of shapes. In particular embodiments,current signal 432 may have a DC offset or may include current pulseshaving any suitable shape, such as for example, square-shaped pulses,triangle-shaped pulses, Gaussian-shaped pulses, or pulses having anarbitrary shape or a combination of shapes. The pulses of current signal432 may have a shape or duration similar to that of voltage signal 422.Additionally, laser diode 440 may emit optical pulses with a shape(e.g., square, triangle, Gaussian, or arbitrary) or duration that atleast approximately corresponds to the shape or duration of the currentpulses supplied by pulse generator 430.

In particular embodiments, laser diode 440 may be a Fabry-Perot laserdiode, a DFB laser, or a DBR laser. As an example, laser diode 440 maybe a DFB laser coupled to an optical fiber or a DFB laser configured toemit a free-space output beam. Additionally, the light emitted by laserdiode 440 may pass through an optical isolator that reduces the amountof back-reflected light that may be coupled back into the laser diode440. In particular embodiments, seed laser 400 may include a singlelaser diode 440 having a substantially fixed operating wavelength. As anexample, laser diode 440 may be a single-wavelength laser configured tooperate at a particular operating wavelength with limited wavelengthtunability. As another example, laser diode 440 may include a DFB laserwith an operating wavelength between approximately 1400 nm and 1600 nm,and the DFB laser may be wavelength tunable over a range ofapproximately 4 nm (e.g., by adjusting the operating temperature of thelaser diode 440).

In particular embodiments, laser diode 440 may operate withouttemperature control, or seed laser 400 may include a temperaturecontroller 450 to stabilize the operating temperature of laser diode440. As an example, the package or the semiconductor substrate of laserdiode 440 may be thermally coupled to a thermoelectric cooler (TEC)driven by temperature controller 450 to adjust or stabilize thelaser-diode operating temperature. The laser-diode operating temperaturemay be stabilized to within any suitable range of a target temperatureset point, such as for example, within approximately ±0.01° C., ±0.05°C., ±0.1° C., ±0.5° C., or ±1° C. of a target temperature. Stabilizationof the temperature of laser diode 440 may provide for the laser-diodeoperating wavelength to be substantially stable (e.g., the peakwavelength of laser diode 440 may vary by less than any suitable value,such as for example, less than approximately 0.1 nm, 0.5 nm, 1 nm, or 2nm). If lidar system 100 includes a narrow-band optical filter, then thelaser diode 440 may be temperature stabilized so as to match thelaser-diode operating wavelength to the passband of the optical filter.In particular embodiments, the temperature controller 450 may be used toadjust the operating wavelength of laser diode 440 by adjusting thelaser-diode set-point temperature. As an example, the laser diode 440may include a DFB laser with an operating wavelength that may betemperature tuned from approximately 1548 nm to approximately 1552 nm byadjusting the temperature set-point of the laser.

In particular embodiments, seed laser 400 may include awavelength-tunable laser configured to produce light at multiplewavelengths. As an example, a wavelength-tunable laser may produceoptical pulses at multiple wavelengths of light which are sent tomultiple respective sensor heads of a lidar system 100. In particularembodiments, laser diode 440 may be a wavelength-tunable laser. As anexample, laser diode 440 may have an operating wavelength that may betunable over any suitable wavelength range, such as for example, 1 nm,10 nm, 20 nm, 50 nm, or 100 nm. As another example, laser diode 440 maybe tunable from approximately 1400 nm to approximately 1440 nm or fromapproximately 1530 nm to approximately 1560 nm. In particularembodiments, laser diode 440 may be an external-cavity diode laser whichincludes a laser diode and a wavelength-selective element, such as forexample, an external diffraction grating or a grating structureintegrated within the semiconductor structure of the laser diode. Inparticular embodiments, laser diode 440 may be configured to produceoptical pulses at multiple wavelengths. As an example, laser diode 440may produce sequences of pulses having N different wavelengths. Thepulses may be amplified and each pulse may be conveyed to one or moreparticular sensor heads based on the wavelength of the pulse.

FIG. 9 illustrates an example seed laser 400 with multiple laser diodes(440-1, 440-2, . . . , 440-N) that are combined together by amultiplexer 412. In particular embodiments, seed laser 400 may includemultiple laser diodes 440 configured to operate at multiple differentwavelengths and an optical multiplexer 412 configured to combine thelight produced by each laser diode 440 into a single output opticalfiber. As an example, seed laser 400 may include N laser diodes 440configured to operate at N different wavelengths. In particularembodiments, each laser diode 440 may be a pulsed laser diode driven bya separate pulse generator 430 (not illustrated in FIG. 9). As anexample, N separate pulse generators 430 may each be driven or triggeredby a separate function generator 420 (not illustrated in FIG. 9). Thefunction generators 420 may operate independently or may be synchronizedwith respect to one another so that the pulses can be emitted with aparticular time delay between successive pulses. As another example, theN pulse generators 430 may be driven by a single function generator 420that has N trigger-signal outputs. Additionally, the function generator420 may have N-1 electrical delays so that the pulses from each laserdiode 440 can be synchronized or time-delayed with respect to oneanother. In particular embodiments, any suitable number of functiongenerators 420, pulse generators 430, or electrical delays may beintegrated together into a single device.

In particular embodiments, multiplexer 412 may be referred to as awavelength combiner, a mux, or a wavelength-division multiplexer (WDM).In particular embodiments, multiplexer 412 may include an optical-powersplitter, an optical switch, a wavelength multiplexer configured tocombine different wavelengths of light, or any suitable combinationthereof. Multiplexer 412 may have N input ports coupled to N laserdiodes 440, and multiplexer 412 may combine light from the input portstogether into a single output port. In particular embodiments, a N×1multiplexer 412 may perform wavelength combining using a prism,diffraction grating, holographic grating, arrayed waveguide grating, orone or more dichroic filters. In particular embodiments, seed laser 400may include N optical amplifiers (not illustrated in FIG. 9). As anexample, each laser diode 440 may be coupled to an optical amplifierlocated between the laser diode and the multiplexer 412. The opticalamplifiers may be configured to amplify the light from each laser diode440 separately prior to combining in multiplexer 412.

In particular embodiments, the N laser diodes 440 may produce opticalpulses at N respective wavelengths, and each laser diode 440 may producepulses at a pulse repetition frequency f. Additionally, the pulsesproduced by each of the laser diodes 440 may be synchronized so thatafter being combined together by multiplexer 412 the output seed pulsesinclude N sets of time-interleaved pulses which are substantially evenlyspaced in time. As an example, each laser diode 440 may emit pulses thatare delayed with respect to pulses from a preceding laser diode 440 by atime delay of 1/(f×N). The pulses from the N laser diodes 440 may becombined by the N×1 multiplexer 412, resulting in an output seed-laserrepetition frequency of f×N. As an example, seed laser 400 may includeN=8 laser diodes 440, and each laser diode 440 may produce pulses at af=640-kHz pulse repetition frequency with a time delay relative topulses emitted by a preceding laser diode 440 of 1/(640 kHz×8)≅195 ns.This results in an output seed-laser repetition frequency ofapproximately 5.12 MHz with a pulse period of approximately 195 ns. Inparticular embodiments, the output seed-laser pulses may be sent to afiber-optic amplifier for amplification. A fiber-optic amplifier mayexhibit improved performance (e.g., reduced amplified spontaneousemission) when amplifying the output seed-laser pulses due to the higherpulse repetition frequency and higher duty cycle provided by combiningpulses from multiple laser diodes 440 into a single pulse stream foramplification. Additionally, undesirable nonlinear effects in opticalfiber may be reduced or avoided by interleaving the pulses in atime-synchronized manner so that the pulses do not overlap in time.

FIG. 10 illustrates an example light source 110 that includes a seedlaser 400 and an amplifier 470. In particular embodiments, a lightsource 110 may include one or more seed lasers 400 or one or moreamplifiers 470. In particular embodiments, seed laser 400 may include(1) a laser diode (e.g., a DFB laser) driven by a pulse generator 430,(2) a wavelength-tunable laser configured to produce light at multiplewavelengths, (3) multiple laser diodes 440 configured to produce lightat multiple respective wavelengths, or (4) any other suitable lasersource. In particular embodiments, seed laser 400 may produce low-poweroptical pulses, and one or more optical amplifiers 470 may be configuredto amplify the low-power pulses to produce amplified pulses of light.The amplified pulses of light may be emitted as output beam 125. As anexample, amplifier 470 may receive optical seed pulses having an averagepower of greater than or equal to 1 microwatt, and the amplified outputpulses from the amplifier 470 may have an average power of greater thanor equal to 1 mW. As another example, amplifier 470 may receive opticalseed pulses having a pulse energy of greater than or equal to 1 pJ, andthe amplified output pulses from the amplifier 470 may have a pulseenergy of greater than or equal to 0.1 μJ.

In particular embodiments, an amplifier 470 may be referred to as afiber amplifier, optical amplifier, fiber-optic amplifier, optical amp,or amp. In particular embodiments, all or part of an amplifier 470 maybe included in light source 110. In particular embodiments, an amplifier470 may include any suitable number of optical-amplification stages. Asan example, an amplifier 470 of a lidar system 100 may include 1, 2, 3,4, or 5 optical-amplification stages. In particular embodiments,amplifier 470 may include a single-pass amplifier in which light makesone pass through the amplifier 470. In particular embodiments, amplifier470 may include a double-pass amplifier in which light makes two passesthrough the amplifier gain medium. In particular embodiments, amplifier470 may act as a preamplifier (e.g., an amplifier that amplifies seedpulses from a laser diode 440 or a seed laser 400), a mid-stageamplifier (e.g., an amplifier that amplifies light from anotheramplifier), or a booster amplifier (e.g., an amplifier that sends afree-space output beam 125 to a scanner 120). A preamplifier may referto the first amplifier in a series of two or more amplifiers, a boosteramplifier may refer to the last amplifier in a series of amplifiers, ora mid-stage amplifier may refer to any amplifier located between apreamplifier and a booster amplifier.

In particular embodiments, amplifier 470 may provide any suitable amountof optical power gain, such as for example, a gain of approximately 5dB, 10 dB, 20 dB, 30 dB, 40 dB, 50 dB, 60 dB, or 70 dB. As an example,amplifier 470 (which may include two or more separate amplificationstages) may receive pulses with a 1-μW average power and produceamplified pulses with a 5-W average power, corresponding to an opticalpower gain of approximately 67 dB. As another example, amplifier 470 mayinclude two or more amplification stages each having a gain of greaterthan or equal to 20 dB, corresponding to an overall gain of greater thanor equal to 40 dB. As another example, amplifier may include threeamplification stages (e.g., a preamplifier, a mid-stage amplifier, and abooster amplifier) having gains of approximately 30 dB, 20 dB, and 10dB, respectively, corresponding to an overall gain of approximately 60dB.

In particular embodiments, an optical fiber, which may convey, carry,transport, or transmit light from one optical component to another, maybe referred to as a fiber-optic cable, a fiber, an optical link, afiber-optic link, or a fiber link. An optical fiber may includesingle-mode (SM) fiber, large-mode-area (LMA) fiber, multi-mode (MM)fiber, polarization-maintaining (PM) fiber, photonic-crystal orphotonic-bandgap fiber, gain fiber (e.g., rare-earth-doped optical fiberfor use in an optical amplifier), multi-clad fiber (e.g., a double-cladfiber having a core, inner cladding, and outer cladding), or any othersuitable optical fiber, or any suitable combination thereof. As anexample, an optical fiber may include a glass SM fiber with a corediameter of approximately 8 μm and a cladding diameter of approximately125 μm. As another example, an optical fiber may include aphotonic-crystal fiber or a photonic-bandgap fiber in which light isconfined or guided by an arrangement of holes distributed along thelength of a glass fiber. In particular embodiments, one end of anoptical fiber may be coupled to, attached to, or terminated at an outputcollimator. An output collimator may include a lens, a GRIN lens, or afiber-optic collimator that receives light from a fiber-optic cable andproduces a free-space optical beam 125. In FIG. 10, an optical fiber mayconvey optical pulses amplified by amplifier 470 to an output collimatorthat produces a free-space optical beam 125.

FIG. 11 illustrates an example double-pass fiber-optic amplifier 470. Inparticular embodiments, an optical amplifier 470 may receive light atits input, amplify the input light, and send the amplified light to anoutput. The received input light may include optical pulses from a seedlaser 400 or from a previous amplification stage (e.g., two or moreamplifiers 470 may be coupled together in series). The amplified outputlight may be sent to another amplifier 470 (e.g., to provide anotherstage of amplification), a demultiplexer (e.g., for distribution tomultiple optical links or multiple sensor heads), an optical link (e.g.,a fiber-optic cable), a sensor head, or a scanner 120. In particularembodiments, an amplifier 470 may be part of a master oscillator poweramplifier (MOPA) or master oscillator fiber amplifier (MOFA) in which amaster oscillator (e.g., a seed laser 400) sends relatively low-poweroptical pulses to one or more optical amplifiers 470 for amplification.As an example, an amplifier 470 may receive pulses with an input pulseenergy (E_(in)) of approximately 10 pJ and produce amplified pulses withan output pulse energy (E_(out)) of approximately 10 nJ. The opticalgain (G) of the amplifier 470 in decibels, which may be determined fromthe expression G=10 log(E_(out)/E_(in)), is approximately 30 dB. Asanother example, an amplifier 470 may receive input pulses with a peakpower (P_(in)) of approximately 10 W and produce amplified output pulseswith a peak power (P_(out)) of approximately 1 kW. The optical gain (G)of the amplifier 470, which may be determined from the expression G=10log(P_(out)/P_(in)) is approximately 20 dB.

In particular embodiments, an optical amplifier 470 may include one ormore circulators 510, one or more couplers (600A, 600B), one or morephotodiodes (PD 610A, PD 610B), one or more isolators (620A, 620B), oneor more filters 630, one or more pump lasers 640, one or more pump WDMs650, one or more gain fibers 660, or one or more reflectors 670. Thedouble-pass amplifier 470 illustrated in FIG. 11 includes an inputcoupler 600A and photodiode (PD) 610A, an input isolator 620A, acirculator 510, a pump laser 640 and pump WDM 650, a gain fiber 660, areflector 670, an output isolator 620B, an output coupler 600B and PD610B, and an output filter 630. In particular embodiments, circulator510 may be a three-port fiber-optic component that directs light thatenters at one port out to another port. In FIG. 11, light entering atport 1 of the circulator 510 is directed to port 2, and light enteringat port 2 is directed to port 3. In the example of FIG. 11, afterpassing through the coupler 600A and isolator 620A, the input light isdirected from port 1 to port 2 of circulator 510 and then travelsthrough pump WDM 650 and gain fiber 660. The light is reflected byreflector 670 and travels back through gain fiber 660 and pump WDM 650.During the two passes through the gain fiber 660, the input lightundergoes amplification through a process of stimulated emission. Theamplified light is directed from port 2 to port 3 of the circulatorwhere it then travels through isolator 620B, coupler 600B, and filter630. The amplified light is directed to the output of amplifier 470, atwhich point the amplified output light may be sent to another amplifier470, a demultiplexer, an optical link, a sensor head, or a scanner 120.

In particular embodiments, a fiber-optic amplifier 470 may include again fiber 660 that is optically pumped (e.g., provided with energy) bya pump laser 640. The optically pumped gain fiber 660 provides opticalgain to particular wavelengths of light traveling through the gain fiber660. The pump light and the light to be amplified may both propagatesubstantially through the core of the gain fiber 660. The gain fiber 660(which may be referred to as optical gain fiber) may be an optical fiberdoped with rare-earth ions, such as for example erbium (Er³⁺), neodymium(Nd³⁺), ytterbium (Yb³⁺), praseodymium (Pr³⁺), holmium (Ho³⁺), thulium(Tm³⁺), or any other suitable rare-earth element, or any suitablecombination thereof. The rare-earth dopants (which may be referred to asgain material) absorb light from the pump laser 640 and are “pumped” orpromoted into excited states that provide amplification to particularwavelengths of light through stimulated emission. The rare-earth ions inexcited states may also emit photons through spontaneous emission,resulting in the production of amplified spontaneous emission (ASE)light by amplifier 470. In particular embodiments, an amplifier 470 witherbium-doped gain fiber 660 may be referred to as an erbium-doped fiberamplifier (EDFA) and may be used to amplify light having wavelengthsbetween approximately 1520 nm and approximately 1600 nm. In particularembodiments, a gain fiber 660 may be doped with a combination of erbiumand ytterbium dopants and may be referred to as a Er:Yb co-doped fiber,Er:Yb:glass fiber, Er:Yb fiber, Er:Yb-doped fiber,erbium/ytterbium-doped fiber, or Er/Yb gain fiber. An amplifier 470 withEr:Yb co-doped gain fiber may be referred to as anerbium/ytterbium-doped fiber amplifier (EYDFA). An EYDFA may be used toamplify light having wavelengths between approximately 1520 nm andapproximately 1620 nm. In particular embodiments, a gain fiber 660 dopedwith ytterbium may be part of a ytterbium-doped fiber amplifier (YDFA).A YDFA may be used to amplify light having wavelengths betweenapproximately 1000 nm and approximately 1130 nm. In particularembodiments, a gain fiber 660 doped with thulium may be part of athulium-doped fiber amplifier (TDFA). A TDFA may be used to amplifylight having wavelengths between approximately 1900 nm and approximately2100 nm.

In particular embodiments, a fiber-optic amplifier 470 may refer to anamplifier where light is amplified while propagating through a gainfiber 660 (e.g., the light is not amplified while propagating as afree-space beam). In particular embodiments, an amplifier 470 where thelight being amplified makes one pass through a gain fiber 660 may bereferred to as a single-pass amplifier 470 (as described below), and anamplifier 470 where the light being amplified makes two passes through again fiber 660 (as illustrated in FIG. 11) may be referred to as adouble-pass amplifier 470. In particular embodiments, the length of gainfiber 660 in an amplifier 470 may be 0.5 m, 1 m, 2 m, 4 m, 6 m, 10 m, 20m, or any other suitable gain-fiber length. In particular embodiments,gain fiber 660 may be a single-mode, large-mode-area, or multi-cladoptical fiber with a core diameter of approximately 7 μm, 8 μm, 9 μm, 10μm, 12 μm, 20 μm, 25 μm, or any other suitable core diameter. Thenumerical aperture (NA), composition, or refractive indices of thecomponents of an optical fiber may be configured so that the opticalfiber remains in single-mode operation for at least some of thewavelengths of light propagating through the fiber. In the example ofFIG. 11 (as well as some of the other figures described herein), a lineor an arrow between two optical components may represent a fiber-opticcable. As an example, coupler 600A and isolator 620A may be coupledtogether by a fiber-optic cable represented by the arrow that connectsthe two components. As another example, the input and output portsillustrated in FIG. 11 may each represent a fiber-optic cable.

In particular embodiments, pump laser 640 may produce light at anywavelength suitable to provide optical excitation to the dopants of gainfiber 660. As an example, pump laser 640 may be a fiber-coupled orfree-space laser diode with an operating wavelength of approximately 910nm, 915 nm, 940 nm, 960 nm, 976 nm, 980 nm, 1050 nm, 1064 nm, 1450 nm,or 1480 nm. As another example, an erbium-doped gain fiber 660 may bepumped with a 976-nm laser diode. As another example, anerbium/ytterbium-doped gain fiber 660 may be pumped with a laser diodehaving an operating wavelength between approximately 915 nm andapproximately 970 nm. In particular embodiments, pump laser 640 may beoperated as a CW light source and may produce any suitable amount ofaverage optical pump power, such as for example, approximately 100 mW,500 mW, 1 W, 2 W, 5 W, 10 W, 15 W, or 20 W of pump power. In particularembodiments, a pump laser diode may be referred to as a pump diodelaser, a pump laser, a pump diode, or a pump.

In particular embodiments, light from pump laser 640 may be coupled intogain fiber 660 via a pump wavelength-division multiplexer (WDM) 650. Apump WDM 650, which may be referred to as a pump-signal combiner, a pumpcombiner, a wavelength combiner, or a WDM may be used to combine pumplight with input light that is to be amplified. In particularembodiments, a pump WDM 650 may be a three-port or a four-port device.For example, a pump WDM 650 may be a four-port device that combinesinput light received at a first port with light from two pump lasers 640(received at second and third ports, respectively), and sends thecombined light out a fourth port (which may be coupled to gain fiber660). In FIG. 11, the pump WDM 650 is a three-port device that combinesinput light at port 1 having a particular wavelength with pump light atport 2 having a different wavelength and sends the combined light outport 3. As an example, the input light may have a wavelength ofapproximately 1530-1565 nm and may be combined by pump WDM 650 withpump-laser light having a wavelength of approximately 915-970 nm. Thecombined light is then coupled to gain fiber 660, where the pump-laserlight pumps the gain fiber 660, and the input light is amplified. Theinput light makes a first pass through the gain fiber, is reflected byreflector 670, and then makes a second pass through the gain fiber 660.The amplified light then passes through pump WDM 650 and back to port 2of the circulator 510 where it is sent to port 3.

In particular embodiments, a fiber Bragg grating (FBG) may refer to afiber-optic component that includes a periodic variation in therefractive index of the fiber core or cladding. The periodicrefractive-index variation may act as a wavelength-dependent reflectoror filter and may include a distributed Bragg reflector, an apodizedgrating, or a chirped fiber Bragg grating. A FBG may be configured toreflect an operating wavelength (e.g., 1550 nm) of the lidar system 100and transmit other wavelengths, or a FBG may be configured to transmitthe lidar-system operating wavelength and reflect other wavelengths. Forexample, filter 630 may include a FBG that transmits light (e.g.,amplified optical pulses from amplifier 470) over a 1548-1552 nmwavelength range and reflects light (e.g., ASE produced by gain fiber660) outside this wavelength range.

In particular embodiments, reflector 670 may include a mirror or a FBG.As an example, reflector 670 may include a metallic or dielectric mirrorconfigured to receive light from gain fiber 660 and reflect the receivedlight back into the gain fiber 660. As another example, reflector 670may include one or more FBGs configured to reflect light correspondingto one or more operating wavelengths of lidar system 100 and transmit orattenuate light that is away from the reflected wavelengths. Forexample, reflector 670 may include a FBG that reflects light fromapproximately 1540 nm to approximately 1560 nm and transmits light overthe wavelength ranges of approximately 1400-1540 nm and approximately1560-1650 nm. In particular embodiments, a double-pass amplifier 470 mayinclude a circulator 510, a gain fiber 660 having a first end and asecond end, and a FBG, where the first end of the gain fiber 660 iscoupled to the circulator 510 and the second end is coupled to the FBG.In FIG. 11, the upper end of gain fiber 660 is coupled to port 2 ofcirculator 510 via pump WDM 650, and the lower end of gain fiber 660 iscoupled to reflector 670, which may include one or more FBGs.

In particular embodiments, reflector 670 may include a FBG that reflectslight at a wavelength of the input light that is received and amplifiedby amplifier 470. As an example, amplifier 470 may receive and amplifypulses of light having a wavelength of approximately 1552 nm, andreflector 670 may include a FBG configured to reflect light at 1552 nm.In particular embodiments, a FBG may have any suitable reflectively(e.g., reflectivity greater than or equal to 50%, 75%, 90%, 95%, 99%, or99.9%) over any suitable bandwidth Δλ, (e.g., Δλ, may be approximately0.1 nm, 0.2 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, 20 nm, or 50 nm). As anexample, reflector 670 may include a FBG with a reflectivity of greaterthan or equal to 99% over a 2-nm bandwidth centered at 1552 nm. Asanother example, reflector 670 may include a FBG with a reflectivity ofgreater than or equal to 90% over a 10-nm bandwidth centered at 1550 nm.In particular embodiments, a reflector 670 may include a FBG with arelatively narrow reflectivity range (e.g., the bandwidth Δλ may be lessthan or equal to 0.1 nm, 0.2 nm, 0.5 nm, 1 nm, or 2 nm), and lidarsystem 100 may include a laser diode 440 that is temperature stabilizedso that its operating wavelength is maintained within the reflectivityrange of the FBG.

In particular embodiments, reflector 670 may include a FBG that reflectslight at one or more operating wavelengths and transmits or attenuateslight that is away from the one or more operating wavelengths. As anexample, the FBG may reflect light from approximately 1555 nm toapproximately 1560 nm, and the FBG may transmit light at wavelengthsoutside that range. In particular embodiments, outside of its range ofreflectivity, a FBG may have a reflectivity of less than or equal to50%, 20%, 10%, 5%, 2%, 1%, 0.5%, or less than any other suitablereflectivity value. As an example, a FBG with a reflectivity range of1555-1560 nm may have a reflectivity of less than or equal to 50% (or, atransmission of greater than or equal to 50%) over the ranges ofapproximately 1455-1555 nm and approximately 1560-1660 nm. In particularembodiments, out-of-band light (e.g., light that is outside thereflectivity range of a FBG) may be substantially transmitted throughthe FBG. In FIG. 11, a reflector 670 that includes a FBG may transmitout-of-band light (e.g., optical noise, such as for example, ASEproduced in gain fiber 660) so that the light is dumped out of thereflector 670 and is not reflected back into the gain fiber 660. Inparticular embodiments, a reflector 670 that includes a FBG may act as aspectral filter by removing greater than or equal to 50%, 60%, 80%, 90%,95%, or 99% of the out-of-band light received by the reflector 670. Asan example, greater than or equal to 90% of ASE light that is producedin the gain fiber 660 and that propagates to reflector 670 may betransmitted through the reflector 670 and effectively removed from theamplifier 470. In particular embodiments, reflector 670 may include aFBG that reflects light at a pump-laser wavelength (e.g., 976 nm). Lightfrom pump laser 640 that is not absorbed in the gain fiber 660 may bereflected by reflector 670 to make a second pass through the gain fiber660. This may result in an improvement in pumping efficiency since agreater fraction of pump-laser light may be absorbed by configuring thepump light to make two passes through the gain fiber 660.

In particular embodiments, coupler 600A may be a fiber-optic splitter ortap coupler that splits off a portion of input light and sends it to PD610A. The remaining light that is not split-off propagates on toisolator 620A. Similarly, coupler 600B may be a tap coupler that splitsoff a portion of output light and sends it to PD 610B with the remaininglight proceeding to filter 630. The tap coupler 600A or 600B may coupleapproximately 0.5%, 1%, 2%, 3%, 5%, 10%, or any other suitablepercentage of light to PD 610A or PD 610B, respectively. As an example,input coupler 600A may split off approximately 10% of the input lightand direct it to PD 610A and send the remaining approximately 90% ofinput light on to the isolator 620A. As another example, output coupler600B may split off approximately 1% of the amplified light and direct itto PD 610B and send the remaining approximately 99% of the amplifiedlight on to the filter 630. In particular embodiments, an amplifier 470may include an input coupler 600A or an output coupler 600B.

In particular embodiments, PD 610A or 610B may be a silicon, germanium,or InGaAs PN or PIN photodiode. In particular embodiments, coupler 600Aand PD 610A may be used to monitor the input light coming into theamplifier 470, and coupler 600B and PD 610B may be used to monitor thelight after amplification. As an example, PD 610A may receive thesplit-off input light from coupler 600A, and PD 610A may generate anelectrical signal based on the received light. Similarly, PD 610B mayreceive the split-off output light from coupler 600B, and PD 610B maygenerate an electrical signal based on the output light. The electricalsignal from PD 610A or PD 610B may be sent to a processor or controller150 for monitoring the status of the input or output light,respectively. If a voltage or current of the electrical signal from PD610A drops below a particular predetermined threshold level, then aprocessor or controller 150 may determine that there is insufficientlight coming into the amplifier 470. The amplifier 470 may be shut downor disabled (e.g., the pump laser 640 may be turned off or the amount oflight it produces may be reduced) to avoid possible damage to theamplifier 470. If a voltage or current of the electrical signal from PD610B drops below a particular predetermined threshold level, then aprocessor or controller 150 may determine that there is a problem withamplifier 470 (e.g., there may be a broken optical fiber, pump laser 640may be failing, or one of the other components in amplifier 470 may befailing). In particular embodiments, signals from PD 610A or PD 610B maybe used to adjust or monitor the gain or output power of amplifier 470.As an example, a ratio of signals from PDs 610A and 610B may be used todetermine the gain of amplifier 470, and the amplifier gain may beadjusted by changing the pump-laser current (which changes the amount ofpump power provided by pump laser 640). As another example, a signalfrom PD 610B may be used to determine the output power of amplifier 470,and the amplifier output power may be adjusted by changing the currentsupplied to pump laser 640.

In particular embodiments, amplifier 470 may include an input opticalisolator 620A or an output optical isolator 620B. An optical isolator620 may include a Faraday rotator, and the operation of an opticalisolator may be based on the Faraday effect where the polarization oflight traveling through the isolator is rotated in the same directionregardless of the direction of travel of the light. In particularembodiments, an optical isolator 620 may be a free-space opticalcomponent or a fiber-coupled component configured to reduce or attenuatebackward-propagating light. Backward-propagating light may originatefrom ASE light from a gain fiber 660 or from optical reflections at oneor more optical interfaces of the components in amplifier 470, and thebackward-propagating light may destabilize or cause damage to a seedlaser 400, laser diode 440 or amplifier 470. Isolators 620A and 620B inFIG. 11 are configured to allow light to pass in the direction of thearrow drawn in the isolator and block light propagating in the reversedirection. In FIG. 11, a laser diode 440 may provide the input light toamplifier 470, and isolator 620A may significantly reduce the amount ofbackward-propagating light that travels back to the laser diode 440. Theoutput of amplifier 470 in FIG. 11 may be coupled to a second amplifier,and isolator 620B may reduce the amount of light from the secondamplifier that propagates back into the amplifier 470.

In FIG. 11, input isolator 620A may allow light to propagate fromcoupler 600A to port 1 of circulator 510, but any light propagating inthe reverse direction may be attenuated. As an example, back-reflectedlight propagating from port 1 of circulator 510 to isolator 620A may beattenuated by greater than or equal to 5 dB, 10 dB, 20 dB, 30 dB, 40 dB,50 dB, or any other suitable attenuation value. As another example, ifisolator 620A attenuates back-reflected light by greater than or equalto 30 dB, then less than or equal to 0.1% of light propagating from port1 of circulator 510 may be transmitted through the isolator 620A and tocoupler 600A. In particular embodiments, circulator 510 may perform anoptical isolation function. As an example, isolator 620A or 620B may notbe included in amplifier 470, and circulator 510 may include one or moreoptical elements that act as an input or output optical isolator.

In particular embodiments, an amplifier 470 may include an opticalfilter 630 located at the amplifier input, an optical filter 630 locatedat the amplifier output, or optical filters 630 located at both theinput and output of amplifier 470. An input optical filter 630 mayreduce the amount of optical noise (e.g., ASE from a previous amplifierstage) at the input to an amplifier 470. An output optical filter 630may reduce the amount of optical noise accompanying the amplifiedoptical pulses that propagate out of amplifier 470. In the example ofFIG. 11, amplifier 470 includes an optical filter 630 located at theoutput of amplifier 470. The output optical filter 630 in FIG. 11 may beconfigured to remove greater than or equal to 80% of the optical noise(e.g., ASE produced by the gain fiber 660) from the output of amplifier470.

FIG. 12 illustrates an example spectrum of an optical signal before andafter passing through a filter 630. In particular embodiments, a filter630 (which may be referred to as an optical filter, a spectral filter,or an ASE filter) may include an absorptive filter, dichroic filter,long-pass filter, short-pass filter, bandpass filter, or FBG. Inparticular embodiments, a filter 630 may be substantially transmissiveto light over a particular range of wavelengths (e.g., a pass-band) andmay substantially block (e.g., through absorption or reflection) thetransmission of light outside of the pass-band range. As an example, afilter 630 may include a dichroic filter (which may be referred to as areflective, thin-film, or interference filter) which includes asubstantially transparent optical substrate (e.g., glass or fusedsilica) with a series of thin-film optical coatings configured totransmit light over a particular wavelength range and reflect otherwavelengths of light. As another example, a filter 630 may include a FBGconfigured to transmit light over a particular pass-band andsubstantially block light outside of the pass-band. In the example ofFIG. 12, the filter is a bandpass filter with a center wavelength ofλ_(C) and a pass-band from λ_(LO) to λ_(HI), which corresponds to afilter bandwidth of Δλ=λ_(HI)−λ_(LO).

In particular embodiments, a filter 630 may have an optical transmission(within a pass-band) of greater than or equal to 50%, 70%, 80%, 90%,95%, 99%, or any other suitable transmission value. Additionally, afilter 630 may have an optical transmission of less than or equal to50%, 20%, 10%, 1%, 0.5%, 0.1%, or any other suitable transmission valuefor wavelengths outside the pass-band. The optical transmission outsidethe pass-band may also be expressed in terms of decibels (dB) ofattenuation. For example, the filter attenuation for wavelengths outsidethe pass-band may be greater than or equal to 3 dB, 10 dB, 15 dB, 20 dB,30 dB, or any other suitable attenuation value. An attenuation value of20 dB corresponds to blocking approximately 99% of the incident lightpower and transmission of approximately 1% of incident light. Inparticular embodiments, a filter 630 may transmit light at one or moreoperating wavelengths of a lidar system 100 and block or attenuate lightaway from the transmitted wavelengths by greater than or equal to 3 dB,10 dB, 15 dB, 20 dB, 30 dB, or any other suitable attenuation value. Thelight that is away from the transmitted wavelengths may refer to lightwith a wavelength outside of a pass-band of the filter 630. As anexample, a filter 630 may transmit greater than or equal to 90% ofincident light within a filter pass-band and may block or attenuatelight outside of the pass-band by 20 dB. As another example, a filter630 may have a filter attenuation of greater than or equal to 20 dB forwavelengths between approximately [λ_(LO)−100 nm] and λ_(LO) andwavelengths between approximately λ_(HI) and [λ_(HI)+100 nm].

In particular embodiments, a filter 630 may have any suitable filterbandwidth Δλ, such as for example, a filter bandwidth of 0.1 nm, 0.2 nm,0.5 nm, 1 nm, 2 nm, 5 nm, or 10 nm. As an example, a filter 630 may havea pass-band with a 1-nm bandwidth that is centered about centerwavelength 1554.9 nm. In particular embodiments, a filter 630 may have arelatively narrow pass-band (e.g., a filter bandwidth Δλ, of less thanor equal to 0.05 nm, 0.1 nm, 0.2 nm, 0.5 nm, or 1 nm), and a laser diode440 of the lidar system 100 may be temperature stabilized so that thelaser-diode operating wavelength is matched to the filter pass-band. Inparticular embodiments, a filter 630 may have a relatively broadpass-band (e.g., a filter bandwidth Δλ, of greater than or equal to 1nm, 2 nm, 5 nm, 10 nm, 20 nm, or 50 nm), and a laser diode 440 may notrequire temperature stabilization to maintain its operating wavelengthwithin the filter pass-band.

In particular embodiments, an optical spectrum before passing through afilter 630 may include a signal spectrum along with background opticalnoise, which may include amplified spontaneous emission (ASE)originating from an amplifier 470. In FIG. 12, the signal spectrum,which may represent the spectrum for a series of optical pulses, iscentered at wavelength λ_(C) and has a bandwidth of δλ. The signalspectrum is contained within the pass-band of the filter and passesthrough the filter with little or no attenuation (e.g., ≤10%attenuation). Similarly, the optical pulses associated with the signalspectrum may pass through the filter with little or no attenuation ordistortion to their shape. In FIG. 12, the optical spectrum beforepassing through the filter includes a broadband offset associated withASE. In particular embodiments, an ASE spectrum may extend over awavelength range of approximately 20 nm, 40 nm, 60 nm, or 80 nm (e.g.,from approximately 1510 nm to approximately 1590 nm). The portion of theASE that falls outside the filter pass-band may be substantiallyattenuated, as indicated by the after-filter spectrum illustrated inFIG. 12 where wavelengths less than λ_(LO) and greater than λ_(HI) areattenuated after passing through the filter. In particular embodiments,a filter 630 may be used to reduce or substantially remove unwantedoptical signals or noise (e.g., ASE) from a light source 110, seed laser400, or amplifier 470 of a lidar system 100. As an example, a filter 630may be located at or near an output of an optical amplifier 470, and thefilter may be configured to remove any suitable amount of the ASE fromthe amplifier output 470, such as for example, 50%, 60%, 80%, 90%, 95%,or 99% of the ASE. As another example, a filter with a 1-nm bandwidththat receives a signal with background optical noise that extends overapproximately 50 nm may remove approximately 94% to 98% of thebackground noise from the signal.

In particular embodiments, a filter 630 may have a single pass-band(e.g., 1550-1552 nm) or two or more distinct pass-bands (e.g., 1550-1552nm and 1555-1557 nm). As an example, for a lidar system 100 with Noperating wavelengths, a filter may have N pass-bands corresponding toeach of the N operating wavelengths. In particular embodiments, thecenter wavelength λ_(C) or the bandwidth δλ of a filter may besubstantially fixed. In particular embodiments, a filter 630 may have anadjustable center wavelength λ_(C) or an adjustable bandwidth δλ. As anexample, the center wavelength of a filter may be dynamically changed tomatch the changing wavelength of a wavelength-tunable seed laser 400 orlaser diode 440.

FIG. 13 illustrates an example single-pass fiber-optic amplifier 470. InFIG. 13, input light makes a single pass through the gain fiber 660, andafter passing through the output of amplifier 470, the amplified outputlight may be sent to another amplifier 470, a demultiplexer, an opticallink, a sensor head, or a scanner 120. In particular embodiments, asingle-pass amplifier 470 may include one or more optical filters (e.g.,630A or 630B), couplers (e.g., 600A or 600B), photodiodes (e.g., 610A or610B), isolators (e.g., 620A or 620B), gain fibers 660, pump lasers(e.g., 640A or 640B), or pump WDMs (e.g., 650A or 650B). The single-passamplifier 470 illustrated in FIG. 13 has an input that includes an inputfilter 630A, an input coupler 600A and PD 610A, and an input isolator620A. The optical gain for the amplifier 470 is provided by pump lasers640A and 640B which are coupled to gain fiber 660 through pump WDMs 650Aand 650B, respectively. The gain fiber 660 in FIG. 13 may be anerbium-doped or erbium/ytterbium-doped gain fiber 660. The single-passamplifier 470 illustrated in FIG. 13 has an output that includes anoutput isolator 620B, an output coupler 600B and PD 610B, and an outputfilter 630B.

In particular embodiments, an amplifier 470 may include 1, 2, 3, or anyother suitable number of pump lasers 640. The double-pass amplifier 470in FIG. 11 includes one pump laser 640, and the single-pass amplifier470 in FIG. 13 includes two pump lasers (640A, 640B). In particularembodiments, a double-pass amplifier 470 may include one pump laser 640(as illustrated in FIG. 11), or a double-pass amplifier 470 may includetwo pump lasers 640 (e.g., one pump laser coupled to each end of thegain fiber 660). In particular embodiments, a single-pass amplifier 470may have one pump laser (e.g., pump laser 640A or 640B), or asingle-pass amplifier 470 may have two pump lasers (e.g., pump lasers640A and 640B). In particular embodiments, a pump laser may beco-propagating or counter-propagating with respect to the light that isamplified by an amplifier 470. In FIG. 13, pump laser 640A is aco-propagating pump laser (e.g., the pump-laser light propagates in thesame direction as the light that is amplified by the amplifier 470), andpump laser 640B is a counter-propagating pump laser (e.g., thepump-laser light propagates in the opposite direction to the light thatis amplified). In particular embodiments, one pump laser may be used toprovide pump light to both ends of a gain fiber 660. As an example, pumplaser 640A in FIG. 13 may be split (e.g., with a 3-dB fiber-optic powersplitter) into two fibers, where one fiber is coupled to pump WDM 650Aand the other fiber is coupled to pump WDM 650B.

FIG. 14 illustrates an example booster amplifier 470 that produces afree-space output beam 125. In particular embodiments, a boosteramplifier 470 may refer to an amplifier that sends an output beam 125 toa scanner 120 or a sensor head, or a booster amplifier 470 may refer toan amplifier that provides an intermediate or final amplification stagein a series of two or more amplifiers. As an example, booster amplifier470 in FIG. 14 may receive optical pulses that have been amplified byone or more previous amplifiers (e.g., a single-stage amplifier 470 or adouble-stage amplifier 470). A booster amplifier 470 may send amplifiedlight to another booster amplifier 470 for further amplification, or abooster amplifier 470 may produce a free-space output beam 125 that isdirected to a scanner 120 or a sensor head. As another example, boosteramplifier 470 may receive unamplified optical pulses (e.g., from apulsed laser diode), and booster amplifier 470 may provide a singlestage of optical amplification prior to sending a free-space output beam125 to a scanner 120. As another example, two booster amplifiers 470 maybe coupled in series where the first amplifier amplifies input light(e.g., from a pulsed laser diode or from a previous amplifier stage) andsends it to the second amplifier, and the second amplifier furtheramplifies the light and produces a free-space output beam 125. Inparticular embodiments, a booster amplifier 470 may include an outputcollimator 340 configured to receive amplified optical pulses producedin gain fiber 660 and produce a free-space optical beam 125 thatincludes the amplified optical pulses. As an example, the boosteramplifier 470 in FIG. 14 may be a fiber-optic amplifier that isterminated at output collimator 340, and output collimator 340 mayproduce a free-space output beam 125.

In particular embodiments, a booster amplifier 470 may provide anysuitable amount of optical power gain, such as for example, a gain ofapproximately 3 dB, 5 dB, 7 dB, 10 dB, 15 dB, 20 dB, or 30 dB. As anexample, a booster amplifier 470 may receive pulses with a 100-mWaverage power and produce amplified pulses with a 1-W average power,corresponding to an optical gain of approximately 10 dB. In particularembodiments, a booster amplifier 470 may include a single pump laser 640(e.g., a co-propagating or counter-propagating pump laser) or two ormore pump lasers 640 (e.g., two co-propagating pump lasers, or aco-propagating pump and a counter-propagating pump). As an example, abooster amplifier 470 may include a counter-propagating pump laser 640located on the output side of the amplifier 470. In FIG. 14, the boosteramplifier 470 includes a co-propagating pump laser 640 (along with apump WDM 650) located on the input side of the amplifier 470.

In particular embodiments, a booster amplifier 470 may include amulti-clad gain fiber 660 that includes two or more cladding layers(e.g., a double-clad gain fiber 660 or a triple-clad gain fiber 660). Inparticular embodiments, a double-clad gain fiber 660 may include a core,inner cladding, and outer cladding, where the core is doped with arare-earth material. As an example, the core may be doped with erbium,or the double-clad gain fiber 660 may be a Er:Yb co-doped fiber wherethe core is doped with a combination of erbium and ytterbium. Therefractive indices of the core, inner cladding, and outer cladding maybe configured so that the pump-laser light is confined to propagateprimarily in the inner cladding, and the amplified light is confined topropagate primarily in the core. In particular embodiments, adouble-clad gain fiber 660 may have a core with any suitable diameter,such as for example, a diameter of approximately 7 μm, 8 μm, 9 μm, 10μm, 12 μm, 20 μm, or 25 μm. In particular embodiments, gain fiber 660may be a double-clad photonic-crystal fiber that includes a core dopedwith rare-earth material where the core is surrounded by an arrangementof holes that extend along the length of the gain fiber 660.

In particular embodiments, amplifier 470 may include a cladding powerstripper 680, which may also be referred to as a cladding mode stripper.A cladding power stripper 680 may be used to absorb or remove light fromthe inner cladding or outer cladding in a double-clad gain fiber 660. Asan example, cladding power stripper 680 may be located on the oppositeside of the gain fiber 660 from the pump laser 640, and the claddingpower stripper 680 may remove residual, unabsorbed pump-laser light thatpropagates through the gain fiber 660 without being absorbed in the gainfiber 660. As an example, the residual pump-laser light may be removedfrom the inner cladding of the gain fiber 660 to prevent the residualpump light from accompanying the amplified pulses as they exit theamplifier 470. Additionally, the cladding power stripper 680 may removeASE produced by the gain fiber 660 that propagates in the inner or outercladding.

FIG. 15 illustrates a top view of an example free-space pre-amplifierassembly 700. The pre-amplifier assembly 700 illustrated in FIG. 15 maybe referred to as a fiber laser, fiber laser with free-space components,free-space amplifier, pre-amplifier, laser system, laser, or lightsource and may be part of a light source 110 of a lidar system 100. Inthe example of FIG. 15 (as well as some of the other figures describedherein), a line or an arrow between two optical components may representa free-space optical beam. As an example, the arrow that extends fromseed laser diode 710 to combiner 750 (and through seed-laser lens 720and optical isolator 722) represents a free-space optical beam emittedby the seed laser diode 710. Similarly, the arrow that extends from pumplaser diode 730 to combiner 750 (and through pump-laser lens 740)represents a free-space optical beam emitted by the pump laser diode730.

As used herein, a free-space optical beam may refer to an optical beamthat propagates in a non-confined or unguided manner. For example, afree-space optical beam (which may be referred to as a beam or afree-space beam) may propagate through air (or some other gas or avacuum), and a free-space beam may not be confined to propagate in awaveguide or an optical fiber. A free-space component may refer to anoptical component (e.g., lens, isolator, filter, detector, or diodelaser) configured to receive or transmit a free-space beam. A free-spacecomponent, which may be referred to as a free-space optical component, abulk component, a bulk optic, or a bulk optical component, may notinclude a fiber-optic cable. In FIG. 15, seed-laser beam 714, pump-laserbeam 734, and combined beam 752 may each be a free-space optical beam.Additionally, seed-laser lens 720, optical isolator 722, pump-laser lens740, combiner 750, and focusing lens 754 may each be a free-spaceoptical component.

In particular embodiments, a pre-amplifier assembly 700 may include aseed laser diode 710 configured to produce a free-space seed-laser beam714. The seed laser diode 710 in FIG. 15 may be any suitable type oflaser diode, such as for example a Fabry-Perot laser diode, a quantumwell laser, a DBR laser, a DFB laser, a VCSEL, or a wavelength-tunablelaser diode. The seed laser diode 710 may be configured to produce lightat any suitable wavelength, such as for example, at one or morewavelengths between approximately 1400 nm and approximately 1600 nm. Asan example, the seed laser diode 710 may have an operating wavelength ofapproximately 1550 nm. The seed laser diode 710 in FIG. 15 may besimilar to laser diode 440 in FIG. 8. Rather than being packaged in afiber-pigtailed assembly where the seed-laser beam is coupled into anoptical fiber, the seed laser diode 710 in FIG. 15 may include alaser-diode chip that directly emits a free-space optical beam (e.g.,seed-laser beam 714). As an example, the seed laser diode 710 may bemounted to a chip carrier, and the seed-laser beam 714 may be directlyemitted from a front facet of the seed laser diode 710.

In particular embodiments, a pre-amplifier assembly 700 may include apump laser diode 730 configured to produce a free-space pump-laser beam734. The pump laser diode 730 in FIG. 15 may be any suitable type oflaser diode configured to produce light at a wavelength betweenapproximately 900 nm and approximately 1000 nm or between approximately1470 nm and approximately 1490 nm. For example, the pump laser diode 730may be configured to provide optical excitation to the dopants of gainfiber 760 and may have an operating wavelength of approximately 910 nm,915 nm, 940 nm, 960 nm, 976 nm, 980 nm, or 1480 nm. The pump laser diode730 may be operated as a CW light source and may produce any suitableamount of average optical pump power, such as for example, approximately100 mW, 500 mW, 1 W, 2 W, 5 W, 10 W, 15 W, or 20 W of pump power. Thepump laser diode 730 in FIG. 15 may be similar to pump laser 640, 640A,or 640B described herein. Rather than being packaged in afiber-pigtailed package where the pump-laser beam is coupled into anoptical fiber, the pump laser diode 730 in FIG. 15 may include alaser-diode chip that directly emits a free-space optical beam (e.g.,pump-laser beam 734) from a front facet of the pump laser diode 730. Theseed laser diode 710 and the pump laser diode 730 may each be referredto as a free-space laser diode or a direct-emitter laser diode.

In particular embodiments, a pre-amplifier assembly 700 may include aseed-laser lens 720 configured to collect, collimate, or focus afree-space seed-laser beam 714 emitted by seed laser diode 710. As anexample, the seed laser 710 may emit light that diverges into anelliptical cone shape, and the seed-laser lens 720 may collect the lightemitted by the seed laser 710 and produce a collimated optical beam. Inparticular embodiments, a pre-amplifier assembly 700 may include apump-laser lens 740 configured to collect, collimate, or focus afree-space pump-laser beam 734 emitted by pump laser diode 730. Inparticular embodiments, seed-laser lens 720 and pump-laser lens 740 mayeach include any suitable type of lens, such as for example, a sphericallens (e.g., a lens having one or more concave, convex, or planarsurfaces), a cylindrical lens, an aspheric lens, a gradient-index (GRIN)lens (which may be referred to as a graded-index lens), or any suitablecombination thereof. As an example, the seed-laser lens 720 may includea spherical lens or an aspheric lens configured to produce a collimatedseed-laser beam 714 having a substantially circular or elliptical shape.The seed-laser lens 720 and pump-laser lens 740 may each include a lenshaving any suitable size or diameter, such as for example, a diameter ofapproximately 1 μm, 10 μm, 100 μm, 200 μm, 0.5 mm, 1 mm, 2 mm, 5 mm, or10 mm.

In particular embodiments, due to the rectangular shape of the activearea from which the beam is emitted, the output beam from seed laserdiode 710 or pump laser diode 730 may have a substantially ellipticalshape with different divergence angles along two directions. Forexample, the pump laser diode 730 may emit light having a 5°-10°divergence along a horizontal axis and a 20°-40° divergence along avertical axis. The axis with the larger divergence may be referred to asthe “fast axis,” and the axis with the smaller divergence may bereferred to as the “slow axis.” In particular embodiments, seed-laserlens 720 or pump-laser lens 740 may be referred to as a lens assemblyand may include one, two, three, or any other suitable number of lenses.As an example, the pump-laser lens 740 in FIG. 15 may include twolenses, such as for example: a spherical lens and a cylindrical lens;two cylindrical lenses; or a fast-axis collimating lens and a slow-axiscollimating lens. The two lenses may be packaged together into a singlelens assembly that is installed or aligned as one unit, or the twolenses may be discrete elements that are installed or alignedseparately. The pump-laser lens 740 may include a first cylindrical lensthat collimates the pump-laser beam 734 along the fast axis followed bya second cylindrical lens that collimates the pump-laser beam 734 alongthe slow axis. The first cylindrical lens may be referred to as afast-axis collimating lens, and the second cylindrical lens may bereferred to as a slow-axis collimating lens.

In particular embodiments, seed-laser lens 720 or pump-laser lens 740may include a micro-optic lens incorporated into or attached to thefront facet of the seed laser diode 710 or the pump laser diode 730,respectively. For example, a small cylindrical lens epoxied to the frontfacet of the seed laser diode 710 may be configured to act as afast-axis collimating lens by collimating the seed-laser beam 714 alongthe fast axis. A second lens may be located external to the seed laserdiode 710 and may be configured to act as a slow-axis collimating lens.

In particular embodiments, a pre-amplifier assembly 700 may include anoptical isolator 722 configured to transmit light traveling in onedirection and block light from propagating back through the isolator722. As an example, an optical isolator 722 may be used to preventback-reflected light from propagating back to a seed laser 710, a pumplaser 730, or a gain fiber 760. In FIG. 15, the free-space opticalisolator 722 transmits the collimated seed-laser beam 714 and preventslight from propagating back toward the seed laser diode 710. The opticalisolator 722 in FIG. 15 may be a free-space optical isolator thatoperates in a manner similar to a fiber-optic isolator 620 describedabove.

In particular embodiments, a pre-amplifier assembly 700 may include anoptical-beam combiner 750 configured to combine the collimatedseed-laser beam 714 and pump-laser beam 734 into a combined free-spacebeam 752. An optical-beam combiner 750 may be referred to as a beamcombiner, a wavelength combiner, a combiner, a wavelength multiplexer, apump-signal combiner, a pump combiner, a dichroic combiner, or a WDM. Anoptical-beam combiner 750 may be a free-space optical component thatcombines two beams having two different wavelengths (e.g., a free-spaceseed-laser beam 714 and a free-space pump beam 734), and an optical-beamcombiner 750 may operate in a manner similar to a pump WDM 650 describedabove.

In particular embodiments, combiner 750 may be a dichroic beam splittercube or dichroic beam splitter plate. As an example, the combiner 750may be a dichroic beam splitter configured to reflect light from theseed laser 710 and transmit light from the pump laser 730 (or viceversa). In FIG. 15, the combiner 750 is a dichroic beam splitter cubethat reflects the free-space seed-laser beam 714 and transmits thefree-space pump-laser beam 734 to produce the combined free-space beam752. For example, the combiner 750 may reflect light at approximately1530-1560 nm and transmit light at approximately 920-980 nm. As anotherexample, the combiner 750 may reflect light at approximately 1545-1555nm and transmit pump-laser light at approximately 1480 nm. The combinedbeam 752 includes most or all of the light from the seed-laser beam 714and most or all of the light from the pump-laser beam 734, and the twobeams may be combined or overlapped so that they are substantiallycoaxial or coaligned (e.g., the two beams propagate along substantiallythe same propagation axis). The combiner 750 may have any suitable sizeor shape, such as for example, a cuboid shape with a side length ofapproximately 0.5 mm, 1 mm, 2 mm, 5 mm, or 10 mm. As another example,the combiner 750 may have a disk or plate shape with a diameter or sidelength of approximately 0.5 mm, 1 mm, 2 mm, 5 mm, or 10 mm and athickness of approximately 0.1 mm, 1 mm, 2 mm, or 5 mm. In particularembodiments, in addition to combining optical beams, a combiner 750 mayalso act as an optical filter to prevent back-propagating light fromreaching the seed laser diode 710 or the pump laser diode 730. As anexample, ASE produced in the gain fiber 760 may propagate back towardsthe combiner 750. The combiner 750 may reflect most of the ASE, whichprevents the back-propagating ASE from reaching the pump laser diode730.

In particular embodiments, a pre-amplifier assembly 700 may include afocusing lens 754 configured to focus a combined beam 752. Additionally,a pre-amplifier assembly 700 may include an optical gain fiber 760having an input end 768 configured to receive a focused beam. As anexample, the focusing lens 754 may receive the combined beam 752 fromthe combiner 750 and may focus the combined beam 752 onto the input face762 of the gain fiber 760. The input face 762 of the gain fiber 760 maybe configured to receive a focused beam produced by the focusing lens754. The focused beam may be coupled into the gain fiber 760 through theinput face 762 and may then propagate through the gain fiber 760. Thelight received by the input face 762 that propagates through the gainfiber 760 may include light from the pump-laser beam 734 and light fromthe seed-laser beam 714.

In particular embodiments, the input face 762 may be a cleaved orpolished surface of the gain fiber 760. The input face 762 may becleaved or polished so that it is substantially normal to the combinedbeam 752, or the input face 762 may be cleaved or polished at an angleso that it is angled with respect to the combined beam 752. Inparticular embodiments, the input face 762 may include ananti-reflection (AR) coating having a low optical reflectivity at awavelength of seed laser 710 or pump laser 730. As an example, the inputface 762 may be cleaved or polished, and then a dielectric coating maybe deposited onto the surface of the input face 762. The dielectriccoating may be an AR coating with a low optical reflectivity (e.g.,R<1%) at the seed-laser wavelength (e.g., 1545-1555 nm) or at thepump-laser wavelength (e.g., 940-980 nm). Angling the input face 762 orapplying an AR coating to the input face 762 may reduce the amount ofreflected light from the input face 762 that propagates back to the seedlaser diode 710 or the pump laser diode 730. Additionally, applying anAR coating to the input face 762 may increase the amount of light fromthe seed laser 710 or pump laser 730 that is coupled into the gain fiber760.

In particular embodiments, the focusing lens 754 may include one or morelenses (e.g., one or more spherical lenses or aspheric lenses) havingany suitable size or diameter, such as for example, a diameter ofapproximately 1 μm, 10 μm, 100 μm, 200 μm, 0.5 mm, 1 mm, 2 mm, 5 mm, or10 mm. The focusing lens 754 may be similar to seed-laser lens 720 orpump-laser lens 740. The focusing lens 754 may be a discrete opticalelement located some distance (e.g., 1 mm, 2 mm, 5 mm, or 10 mm) fromthe input face 762 of gain fiber 760. In particular embodiments, all orpart of the focusing lens 754 may be combined with or attached to theinput face 762. As an example, the focusing lens 754 may include a GRINlens connected or attached to the input face 762, and the GRIN lens mayreceive the collimated combined beam 752 and focus it into the gainfiber 760. As another example, the input end 768 of gain fiber 760 maybe a lensed fiber (e.g., at least part of the focusing lens 754 isintegrated into the input face 762) where the input face 762 is shaped,tapered, or rounded to act as a lens so that the combined beam 752 isreceived and focused into the gain fiber 760.

In particular embodiments, a pre-amplifier assembly 700 may include anoptical gain fiber 760 having an input end 768, an input face 762, acore 764, and a cladding 766. The input end 768 of the gain fiber 760may refer to a length of the end of the gain fiber 760 that is part of,attached to, located above, or contained within a platform 705 of thepre-amplifier assembly 700. As an example, the gain fiber 760 mayinclude a 2-6 meter length of optical fiber, and a 1-100 mm end portionof the gain fiber 760 may be attached to the platform 705 and may bereferred to as the input end 768 of the gain fiber 760. The input end768 of the gain fiber 760 may be attached to or located on or above theplatform 705, and the remaining length of the gain fiber 760 may belocated outside of or beyond the boundaries of the platform 705. Inparticular embodiments, gain fiber 760 of a pre-amplifier assembly 700may include any suitable type of gain fiber. As an example, the gainfiber 760 may be a single-clad gain fiber (as illustrated in FIG. 15)where light from the seed-laser beam 714 and light from the pump-laserbeam 734 both propagate substantially along the core 764. As anotherexample, the gain fiber 760 may be a multi-clad gain fiber (as describedbelow), such as for example, a double-clad gain fiber or a triple-cladgain fiber, where light from the seed-laser beam 714 propagatessubstantially along the core 764 and light from the pump-laser beam 734propagates substantially along a cladding layer.

In particular embodiments, gain fiber 760 may include a section of relayfiber that is spliced to the gain fiber. The relay fiber may be a lengthof standard optical fiber (e.g., optical fiber that is not doped withgain material) that receives the light from the combined beam 752 andconveys that light to the gain-fiber section of the gain fiber 760. Asused herein, a gain fiber 760 may refer to a length of optical fiberdoped with gain material, or a gain fiber 760 may refer to a combinationof relay fiber and gain fiber (e.g., a length of relay fiber that isspliced to a length of optical fiber doped with gain material). Theundoped relay fiber and the doped fiber together may be referred to as again fiber 760. As an example, the relay fiber may include the inputface 762 and the input end 768 that is attached to or located on orabove the platform, and the relay fiber may be spliced the gain-fibersection. The relay fiber may have any suitable length, such as forexample, a length of approximately 0.1 m, 0.5 m, 1 m, 2 m, or 5 m, andthe gain fiber 760 may have any suitable length, such as for example, alength of approximately 1 m, 2 m, 3 m, 5 m, or 10 m.

In particular embodiments, gain fiber 760 may include a fiber Bragggrating (FBG) configured to reflect a portion of pump-laser light backto the pump laser diode 730. As an example, the FBG may be locatedapproximately 1 meter from the input face 762 in the relay-fiber portionor the gain-fiber portion of gain fiber 760. The FBG may be configuredto stabilize the wavelength of the pump laser diode 730 by reflectingback a portion (e.g., approximately 0.1%, 1%, 2%, 5%, or 10%) of thepump-laser light at a specific wavelength. For example, the FBG mayreflect light at 976 nm±0.5 nm, which acts to stabilize the pump-laserwavelength to within this same wavelength range. Additionally, the FBGmay be substantially transparent to the light produced by the seed laserdiode 710 and may reflect little or none of the seed-laser light.

In particular embodiments, gain fiber 760 may be configured to absorb atleast part of the light from the pump-laser beam 734 and amplify thelight from the seed-laser beam 714. As the light from the pump-laserbeam 734 propagates through the gain fiber 760, most of it may beabsorbed by the gain material (e.g., rare-earth dopants) locatedprimarily in the core 764 of the gain fiber 760. The excited gainmaterial then amplifies the light from the seed-laser beam 714 as itpropagates through the gain fiber 760. In particular embodiments, theseed laser diode 710 may be operated in a pulsed mode. For example, theseed-laser beam 714 may include optical pulses having a pulse durationless than or equal to 100 ns and a duty cycle less than or equal to 10%,and the amplified optical pulses produced after propagating through thegain fiber 760 may have substantially the same pulse duration and dutycycle. As another example, the seed laser 710 may produce pulses with apulse duration of approximately 4 ns at a pulse repetition frequency ofapproximately 600 kHz (corresponding to a duty cycle of approximately0.24%). The optical pulses produced by the seed laser diode 710 may beamplified in gain fiber 760 by any suitable amount of optical power gain(e.g., a gain of approximately 10 dB, 20 dB, 30 dB, or 40 dB). Forexample, the seed-laser pulses may have a pulse energy of approximately0.1 nJ, and after propagating through the gain fiber 760, the pulses mayhave a pulse energy of approximately 0.1 μJ (corresponding to a 30-dBgain).

In particular embodiments, a pre-amplifier assembly 700 may include oneseed laser diode 710 (as illustrated in FIG. 15), or a pre-amplifierassembly 700 may include two or more seed laser diodes 710. As anexample, the pre-amplifier assembly 700 may include two seed laserdiodes 710 having two different operating wavelengths. The seed laserdiodes may operate at 1548 nm and 1552 nm, for example, and a free-spacewavelength combiner (similar to combiner 750) may be used to combine thelight from the two seed lasers. In particular embodiments, the multipleseed lasers of a pre-amplifier assembly 700 may be configured to producetime-interleaved optical pulses. For example, two seed lasers may eachproduce pulses at a 500-kHz pulse repetition frequency, and the pulsesmay be interleaved to form a seed-laser beam 714 with a 1-MHz pulserepetition frequency.

In particular embodiments, a pre-amplifier assembly 700 may include oneor more optical filters. For example, a pre-amplifier assembly 700 mayinclude a bandpass filter that transmits the seed-laser beam 714 andreflects or attenuates light at other wavelengths. The seed laser diode710 may operate at approximately 1550 nm, and a bandpass filter with a1548-1552 nm pass-band may be located between the seed laser diode 710and the combiner 750. The bandpass filter may reduce the amount ofpotentially destabilizing or damaging light (e.g., stray light from thepump laser diode 730 or ASE from the gain fiber 760) that is coupled tothe seed laser diode 710. As another example, a pre-amplifier assembly700 may include a bandpass filter that transmits the pump-laser beam 734and reflects or attenuates light at other wavelengths. The pump laserdiode 730 may operate at approximately 960 nm, and a bandpass filterwith 950-970 nm pass-band may be located between the pump laser diode730 and the combiner 750. As another example, a pre-amplifier assembly700 may include a bandpass filter located between the combiner 750 andthe input face 762 and configured to transmit light at the seed-laserwavelength and light at the pump-laser wavelength.

In particular embodiments, a pre-amplifier assembly 700 may include anelectronic seed-laser driver 718 configured to supply electrical currentto a seed laser diode 710. For example, the seed-laser driver 718 maydrive the seed laser diode 710 with current pulses, and each pulse ofelectrical current may result in the emission of a pulse of light by theseed laser diode 710. Additionally, the seed-laser driver 718 mayprovide temperature control or stabilization for the seed laser diode710. For example, the seed laser diode 710 may be mounted on orthermally coupled to a TEC that is driven or controlled by theseed-laser driver 718. The seed-laser driver 718 may receive anindication of the temperature of the seed laser diode 710 from atemperature sensor and may supply current to the TEC to stabilize theseed-laser temperature. In particular embodiments, a pre-amplifierassembly 700 may include an electronic pump-laser driver 738 configuredto supply electrical current to a pump laser diode 730. For example, thepump-laser driver 738 may drive the pump laser diode 730 with asubstantially constant current (e.g., a direct current, or a DCcurrent). Additionally, the pump-laser driver 738 may providetemperature control for the pump laser diode 730 (e.g., the pump-laserdriver 738 may be coupled to a temperature sensor and TEC for the pumplaser diode 730).

In particular embodiments, the seed-laser driver 718 and the pump-laserdriver 738 may be included in separate circuits or circuit boards, orthe two drivers may be combined together into a single circuit orcircuit board. In particular embodiments, the seed-laser driver 718 orpump-laser driver 738 may be located external to the pre-amplifierassembly 700 and may be electrically coupled to the pre-amplifierassembly 700 by one or more wires, cables, traces on a printed circuitboard (PCB), wire bonds, or any suitable combination thereof. Inparticular embodiments, the seed-laser driver 718 or pump-laser driver738 may be part of the pre-amplifier assembly 700. For example, theseed-laser driver 718 or the pump-laser driver 738 may be mounted orattached to the platform 705. As another example, the pump-laser driver738 may be in thermal contact with the platform 705 so that excess heatproduced by the pump-laser driver 738 flows into the platform 705. Theseed-laser driver 718 or the pump-laser driver 738 may be electricallycoupled to the seed laser diode 710 or the pump laser diode 730 by oneor more wires, cables, PCB traces, wire bonds, or any suitablecombination thereof.

In particular embodiments, the seed-laser driver 718 may be combined orintegrated with the seed laser diode 710, or the pump-laser driver 738may be combined or integrated with the pump laser diode 730. Forexample, the seed-laser driver 718 may be flip-chip mounted to theplatform 705, and the seed laser diode 710 may be mounted to the topsurface of the flip-chip package containing the seed-laser driver 718.The top surface of the flip-chip package may include an InP-basedmaterial which the seed laser diode 710 may be mounted to, and theInP-based material may have a coefficient of thermal expansion (CTE)that substantially matches the CTE of the InGaAsP-based seed laser diode710. Similarly, the top surface of the pump-laser driver 738 may includea GaAs-based material which the AlGaAs-based pump laser diode 730 may bemounted to.

In particular embodiments, a pre-amplifier assembly 700 may include aseed-laser detector 716 configured to receive light emitted from a backfacet of the seed laser diode 710. The seed-laser detector 716 (whichmay be referred to as a back-facet detector or a back-facet monitor) maybe positioned directly behind the seed laser diode 710 (e.g.,approximately 0.1 mm, 1 mm, 2 mm, 5 mm, or 10 mm from the back facet) toreceive at least part of the seed-laser back-facet light 712. Inparticular embodiments, a pre-amplifier assembly 700 may include apump-laser detector 736 configured to receive light emitted from a backfacet of the pump laser diode 730. The pump-laser detector 736 (whichmay be referred to as a back-facet detector or a back-facet monitor) maybe positioned directly behind the pump laser diode 730 to receive atleast part of the pump-laser back-facet light 732. A seed laser diode710 or a pump laser diode 730 may include a semiconductor structure withtwo cleaved surfaces (referred to as a front facet and a back facet)from which laser light is emitted. The front facet or back facet mayhave a dielectric coating that configures the seed laser diode 710 orpump laser diode 730 to emit most of the light from the front facet. Forexample, the back facet of the pump laser diode 730 may include ahigh-reflectivity coating (e.g., R≥90%) that reflects most of thepump-laser light. The pump-laser beam 734 may include ≥90% of the totaloptical power emitted by the pump laser diode 730, and the pump-laserback-facet light 732 may include ≤10% of the total optical power.

The seed-laser detector 716 or the pump-laser detector 736 may include aPN or PIN photodiode (e.g., an InGaAs PIN photodiode). The seed-laserdetector 716 may be a separate component, or the seed-laser detector 716may be combined with the seed laser diode 710 into a single assembly(e.g., the seed-laser detector 716 and the seed laser diode 710 may bemounted onto the same chip carrier). Similarly, the pump-laser detector736 may be a separate component, or the pump-laser detector 736 may becombined with the pump laser diode 730 into a single assembly. Theseed-laser detector 716 may receive some or all of the light emitted bythe seed laser diode 710 from the back facet, and the seed-laserdetector 716 may produce an electrical signal (e.g., a current or avoltage) corresponding to the received seed-laser back-facet light 712.Similarly, the pump-laser detector 736 may receive some or all of thelight emitted by the pump laser diode 730 from the back facet, and thepump-laser detector 736 may produce an electrical signal correspondingto the received pump-laser back-facet light 732.

In particular embodiments, the seed-laser detector 716 may be used tomonitor the performance of the seed laser diode 710. Similarly, thepump-laser detector 736 may be used to monitor the performance of thepump laser diode 730. As an example, the performance of the pump laserdiode 730 may degrade over time (e.g., the output optical power producedby the pump laser diode 730 may gradually decrease over tens, hundreds,or thousands of hours of operation). The amount of optical power in thepump-laser beam 734 may be proportional to the amount of power in thepump-laser back-facet light 732 (e.g., the pump-laser back-facet light732 may have approximately 1% of the power of the pump-laser beam 734).As the amount of optical power in the pump-laser beam 734 drops, thecorresponding electrical signal produced by the pump-laser detector 736may also decrease. The pump-laser driver 738 may receive the signalproduced by the pump-laser detector 736, and in response to detecting adecrease in the signal, the pump-laser driver 738 may increase the drivecurrent supplied to the pump laser diode 730. Increasing the pump-laserdrive current may stabilize or maintain the power of the pump-laser beam734 at a particular level (e.g., 8 watts). If the performance of thepump laser diode 730 continues to degrade, the pump-laser driver 738 maysend a notification (e.g., to controller 150) indicating that the pumplaser diode 730 is degrading or may be close to failure. For example, ifthe current required to maintain the power of the pump-laser beam 734exceeds a particular threshold value (e.g., 10 amps), then thepump-laser driver 738 may send a message or set a flag indicating thestatus of the pump laser diode 730. The controller 150 may send anotification indicating that the pump laser diode 730 is degrading ormay soon fail and the lidar system 100 should be taken in for service(e.g., to replace the pump laser diode 730 or to replace thepre-amplifier assembly 700).

In particular embodiments, two or more components of a pre-amplifierassembly 700 may be combined together into an integrated opticalassembly. As an example, two lenses may be combined together into asingle lens assembly to form a seed-laser lens 720, pump-laser lens 740,or focusing lens 754. Rather than separately positioning and attachingthe two lenses to the platform 705, the two lenses may first beinstalled into a mechanical lens holder, and then the lens assembly maybe positioned and attached to the platform 705 as a single optical unit.As another example, the combiner 750 and the focusing lens 754 may becombined together into a single optical assembly, which may be alignedand attached to the platform 705 as a single unit. As another example,the optical isolator 722, combiner 750, and focusing lens 754 may becombined together into a single optical assembly. Theisolator-combiner-lens assembly may be built using a manufacturingstation that is separate from the pre-amplifier assembly 700, and thenthe combined assembly may be aligned and attached to the platform 705 asa single unit. As another example, the pump-laser lens 740, the combiner750, and the focusing lens 754 may first be aligned and packagedtogether into a single optical assembly, and then the optical assemblymay be aligned and installed onto the platform 705 as a single opticalunit.

In particular embodiments, a pre-amplifier assembly 700 may include aplatform 705 (which may be referred to as a mounting platform, amicro-bench, an optical bench, a micro-optical bench, or a siliconoptical bench), where one or more optical components are mechanicallyattached to the platform 705. In the example of FIG. 15, one or more ofthe following free-space optical components may be mechanically attachedto the platform 705: seed laser diode 710, seed-laser lens 720, pumplaser diode 730, pump-laser lens 740, optical-beam combiner 750,focusing lens 754, optical isolator 722, seed-laser detector 716,pump-laser detector 736, and the input end 768 of optical gain fiber760. Additionally, an optical filter or an optical assembly (e.g., acombination of two or more optical components) may be attached to aplatform 705.

In particular embodiments, an optical component being attached ormechanically attached to a mounting platform 705 may refer to an opticalcomponent being epoxied, bonded, welded, soldered, or mechanicallyfastened to the mounting platform 705. An optical component may bemechanically attached to a mounting platform 705 by any suitableattachment technique, such as for example, by bonding with an adhesiveor epoxy (e.g., using an ultraviolet-cure (UV-cure) adhesive, a two-partepoxy, a thermally conductive epoxy, or an electrically conductiveepoxy), welding, brazing, soldering, mechanical fastening (e.g., withone or more screws), or any suitable combination thereof. As an example,a seed laser diode 710 may be attached to a chip carrier with solder orepoxy, and the chip carrier may be attached to the platform 705 withsolder or thermally conductive epoxy. As another example, a combiner 750may be directly attached to the platform 705 by a UV-cure adhesive, or acombiner 750 may be directly attached to the platform 705 by acombination of UV-cure adhesive and epoxy. The combiner 750 may first bealigned and temporarily attached to the platform 705 using a rapidlycuring UV-cure adhesive (e.g., the adhesive may cure in less than oneminute), and then the combiner 750 may be permanently attached to theplatform using an epoxy (which may require 1-24 hours of cure time). Asanother example, a combiner 750 may first be attached to a carrier(e.g., an aluminum block or mount that the combiner 750 is epoxied to)and then the carrier may be attached to the platform 705 by epoxy,solder, or one or more mechanical fasteners.

In particular embodiments, being attached or mechanically attached to amounting platform 705 may refer to an optical component being directlyor indirectly attached, coupled, or secured to the mounting platform705. As an example, a seed laser diode 710 may be directly attached tothe platform 705, or a seed laser diode 710 may be attached in anindirect manner (e.g., the seed laser diode 710 may be attached to achip carrier, thermoelectric cooler, or other intermediate componentwhich in turn is directly mounted to the platform 705). As anotherexample, a seed-laser lens 720 may be directly attached to the platform705, or a seed-laser lens 720 may be installed into a mechanical lensholder which in turn is directly attached to the platform. As anotherexample, the input end 768 of the gain fiber 760 may be inserted into asleeve assembly (e.g., a mechanical block or tube with a small hole thatthe input end 768 is inserted into) and affixed to the sleeve assembly,and then the sleeve assembly may be directly attached to the platform705.

In particular embodiments, a platform 705 may be made from or mayinclude any suitable material, such as for example, glass (e.g.,borosilicate or fused silica), a ceramic material (e.g., aluminum oxideor a lithium-aluminosilicate glass-ceramic), a semiconductor material(e.g., silicon or polysilicon), metal (e.g., aluminum, copper, or anickel-iron alloy, such as for example Invar), carbon fiber, or anysuitable combination thereof. In particular embodiments, the materialfor a platform 705 may be selected to have a relatively low coefficientof thermal expansion (CTE) or a relatively high thermal conductivity.For example, the platform 705 may be made from a material having a CTEof less than 4×10⁻⁶ K⁻¹, such as for example, a glass material, alithium-aluminosilicate glass-ceramic, Invar, or a silicon-basedmaterial. Having a relatively low CTE may allow the optical componentsmounted to the platform 705 to maintain optical alignment in thepresence of environmental temperature variations. As a result, theoverall performance of the pre-amplifier assembly 700 may remainsubstantially constant (e.g., less than 1%, 5%, or 10% variation inoptical power produced at the output end of the gain fiber 760) as theenvironmental temperature changes. As another example, the platform 705may be made from a material with a thermal conductivity of greater than5 W·m⁻¹·K⁻¹, such as for example, aluminum, copper, or aluminum oxide(Al₂O₃). Having a relatively high thermal conductivity may allow theplatform 705 to dissipate or remove heat produced by some of theelectrical components mounted to the platform 705, such as for example,the seed laser diode 710, the pump laser diode 730, the seed-laserdriver 718, or the pump-laser driver 738. The platform 705 may be inthermal contact with a second material (e.g., a heat sink, heat pipe,heat spreader, another thermally conductive material, a TEC, or forcedair from a fan) so that the excess heat flows from the electricalcomponents to the platform 705, and then to the second material awayfrom the platform 705. As another example, the platform 705 may be madefrom a material having both a relatively low CTE and a relatively highthermal conductivity, such as for example, silicon or polysilicon.Additionally, a silicon or polysilicon material may be doped to providean increased amount of thermal conductivity.

FIG. 16 illustrates an example mechanical-attachment technique based onactive alignment of an optical component. An active-alignment techniquemay refer to the installation and attachment of an optical componentonto a platform 705 using some form of electrical or optical feedback(e.g., a reading on a voltmeter or an optical-power meter). For example,the position of a lens 780 may be adjusted until a beam is alignedthrough an aperture or until the amount of optical power coupled into anoptical fiber is maximized. In particular embodiments, one or moreoptical components may be attached to platform 705 using anactive-alignment technique. As an example, an optical component may beattached to a mechanical alignment tool 786 which is used to preciselyadjust the location or angle of the optical component on the platform705. Once the optical component is positioned in a desired location, theoptical component may be attached to the platform 705 by any suitableattachment technique (e.g., adhesive, epoxy, welding, brazing,soldering, or mechanical fastening).

In the example of FIG. 16, an optomechanical lens assembly is preparedby first attaching a lens 780 to a lens holder 782. As an example, in aseparate assembly operation away from the platform 705, the lens 780(which may be a seed-laser lens, a pump-laser lens, or a focusing lens)may be epoxied into an aluminum lens holder 782. Next, theoptomechanical lens assembly may be temporarily attached to an alignmenttool 786 (e.g., by screwing an end of the alignment tool 786 into athreaded tool receptacle 788). The alignment tool 786 may be coupled toa mechanical positioning fixture (e.g., a multi-axis alignment stageconfigured to translate or adjust the angle of the lens holder 782). Thealignment of the lens 780 may be adjusted with the mechanicalpositioning fixture while making near-field or far-field measurements(e.g., with a camera or other viewing device) that provide feedback tohelp optimize the lens alignment. The position or angular alignment ofthe optomechanical assembly may be adjusted until the lens 780 ispositioned in a desired location (e.g., the position of the lens 780 maybe adjusted until an optical beam achieves a desired alignment,collimation, or focusing or until a particular amount of light iscoupled into an optical fiber). For example, the lens 780 may be movedto optimize the coupling of combined beam 752 into the gain fiber 760 orto optimize the alignment or collimation of the seed-laser beam 714 orthe pump-laser beam 734. A layer of epoxy 784 may be applied between theplatform 705 and the lens holder 782, and when the epoxy 784 is cured,the alignment tool 786 may be removed, leaving the optomechanicalassembly (including the lens 780 and the lens holder 782) attached tothe platform 705.

In particular embodiments, a platform 705 may have any suitable length,width, diameter, or thickness. As an example, a platform 705 may have alength, width, or diameter of approximately 10 mm, 20 mm, 50 mm, 100 mm,or 200 mm, and a platform 705 may have a thickness of approximately 0.1mm, 0.5 mm, 1 mm, 2 mm, 5 mm, or 10 mm. As another example, a platform705 may be made from silicon or polysilicon and have dimensions ofapproximately 60 mm×40 mm×1 mm. As another example, a platform 705 maybe made from Invar or aluminum oxide and have dimensions ofapproximately 80 mm×80 mm×4 mm.

FIG. 17 illustrates an example mechanical-attachment technique based onpassive alignment of an optical component. In particular embodiments, aplatform 705 may include one or more registration features 742 which areused to passively align or position an optical component on the platform705. Rather than applying an active-alignment technique as illustratedin FIG. 16, an optical component may be passively positioned andattached to the platform 705 using one or more registration features742. In particular embodiments, a registration feature 742 (which may bereferred to as a mechanical registration feature, an alignment feature,or a positioning feature) may refer to a mechanical element used toprecisely define the location of an optical component on a platform 705.A registration feature 742 may include a bump, protrusion, or hard stopthat extends above a top plane of the platform 705, or a registrationfeature 742 may include a hole or slot that extends below a top plane ofthe platform 705. A registration feature 742 may have any suitable size,such as for example a length, width, height, thickness, or diameter ofapproximately 0.05 mm, 0.1 mm, 0.5 mm, 1 mm, or 5 mm. A registrationfeature 742 may have any suitable shape, such as for example, acircular, elliptical, square, or rectangular shape. As an example, aregistration feature 742 may be round with a 0.5-mm diameter and mayextend above the plane of the platform 705 by 0.5 mm.

In particular embodiments, one or more optical components may beattached to a platform 705 using a passive-alignment technique. Apassive-alignment technique may refer to the installation and attachmentof an optical component onto a platform 705 using mechanical alignmentfeatures and without the use of electrical or optical feedback toposition the optical component. As an example, an optical component (ora holder or mount that the optical component is attached to) may bepushed up against one or more registration features 742, and then theoptical component may be attached to the platform 705. In particularembodiments, a platform 705 may include one or more mechanicalregistration features 742 configured to define a fixed position on theplatform 705 for one or more of a seed laser diode 710, a seed-laserlens 720, an isolator 722, a seed-laser detector 716, a pump laser diode730, a pump-laser lens 740, a pump-laser detector 736, an optical-beamcombiner 750, a focusing lens 754, an input end 768 of a gain fiber 760,an optical filter, or any other suitable optical element. In FIG. 15,the registration features 742 provide hard stops that define thelocation of the pump laser diode 730 with respect to the platform 705.In FIG. 17, the laser-diode chip 790 is attached to the chip carrier794, and the chip carrier 794 is positioned on the platform 705 based onthe registration features 742A, 742B, and 742C. The laser-diode chip 790may be attached to the chip carrier 794 (by a layer of epoxy 784A) in aseparate assembly operation, and then the laser-diode-chip-carrierassembly may be attached to the platform 705 (by a layer of epoxy 784B)in a location defined by the three registration features 742A, 742B, and742C.

In particular embodiments, a registration feature 742 may include adowel pin or a locating pin that is press-fit into the platform 705 sothat a portion of the pin extends above the top plane of the platform705. As an example, an optomechanical assembly may include two holes (ora hole and a slot) which mate with two dowel pins which are press fitinto the platform 705. The two dowel pins define a precise location forthe optomechanical assembly, and the optomechanical assembly may beattached to the platform 705 using epoxy (or any other suitableattachment technique). In FIG. 17, the three registration features 742A,742B, and 742C may be dowel pins which are press fit into the platform705 so that part of each pin extends above the top plane of the platform705. As an example, a layer of epoxy 784B may be applied to the chipcarrier 794 or platform 705, and then the chip carrier 794 may be placedon the platform 705. A mechanical force may be applied to the chipcarrier 794 so that one edge is in contact with or pushed againstregistration feature 742A and another edge is in contact with or pushedagainst registration features 742B and 742C. In particular embodiments,a registration feature 742 may include a hole or slot in the platform705 into which a dowel pin or locating pin is inserted. For example, anoptomechanical assembly may include two dowel pins press fit into thebottom surface of the assembly, and each dowel pin may be inserted intoa hole or slot in the platform 705.

In particular embodiments, one or more registration features 742 may beformed by a machining operation. For example, a platform 705 may be madefrom a plate of metal or ceramic, and the plate may be machined to formone or more registration features 742. The plate may be machined using amilling machine that removes material from the top surface of the plate,except for the areas where registration features 742 are to be located.For example, removing approximately 0.5 mm of the top surface may formregistration features that extend approximately 0.5 mm above the surfaceof the platform 705.

In particular embodiments, one or more registration features 742 may beformed by photolithography or microfabrication. As an example, theplatform 705 may be made from silicon, polysilicon, or any othersuitable semiconductor or silicon-based material, and one or moreregistration features 742 may be produced through a semiconductormicrofabrication process applied to the platform 705. The locations ofthe registration features 742 may be precisely defined usinglithography, and the registration features 742 may be formed by etching.For example, the top surface of the platform 705 may be coated with alayer of photoresist that is then exposed to UV light transmittedthrough a mask that defines the locations of the registration features742. Portions of the photoresist are removed based on the mask pattern.Then, the surface of the platform 705 is etched to remove some of thematerial from the surface and form the registration features 742. Inparticular embodiments, a microfabrication process may produceregistration features 742 with any suitable dimensional or positioningaccuracy, such as for example, an accuracy of less than or equal to 10nm, 20 nm, 50 nm, 100 nm, 0.5 μm, 1 μm, 5 μm, or 10 μm.

In particular embodiments, an active-alignment technique or apassive-alignment technique may be used to position and attach anysuitable optical component to a platform 705. As an example, all theoptical components in a pre-amplifier assembly 700 may be activelyaligned, all the optical components may be passively aligned, or acombination of active and passive alignment techniques may be used inattaching optical components to a platform 705. In FIG. 15, the seedlaser diode 710, the isolator 722, the pump laser diode 730, thecombiner 750, and the input end 768 of the gain fiber 760 may beattached to the platform 705 using a passive-alignment technique. Theseed-laser lens 720, the pump-laser lens 740, and the focusing lens 754may be attached to the platform 705 using an active-alignment technique.As an example, the seed-laser lens 720 may be attached to a mechanicalpositioning fixture which adjusts the position of the seed-laser lens720 until the collimation, focusing, or alignment of the seed-laser beam714 is optimized. As another example, the position of the focusing lens754 may be adjusted until the coupling of the seed-laser beam 714 orpump-laser beam 734 into the gain fiber 760 is maximized, and then thefocusing lens 754 may be attached to the platform 705.

In particular embodiments, a platform 705 may be contained within anenclosure that includes a feedthrough for optical gain fiber 760. As anexample, after a pre-amplifier assembly 700 is built, the assembly(including the platform 705 and the optical components attached to theplatform 705) may be installed into an enclosure that protects theoptical components from contaminants. The enclosure may be an airtightor watertight structure that prevents water vapor, liquid water, dirt,dust, or other contaminants from getting inside the enclosure. Theenclosure may be configured to be purged with an inert gas (e.g., dryair, nitrogen, or argon) and sealed. The enclosure may include afeedthrough that allows the gain fiber 760 to exit from the enclosure.The feedthrough may be an airtight or watertight feedthrough that allowsthe fiber to exit but still maintains a seal. The enclosure may alsoinclude one or more feedthroughs that allow electrical wire or cables toenter or exit the enclosure.

FIG. 18 illustrates a top view of an example free-spacebooster-amplifier assembly 800. The booster-amplifier assembly 800illustrated in FIG. 18 may be referred to as a fiber laser, fiber laserwith free-space components, free-space amplifier, booster amplifier,power amplifier, amplifier, laser system, laser, or light source, andthe booster-amplifier assembly 800 may be part of a light source 110 ofa lidar system 100. In FIG. 18, input beam 814, pump-laser beam 834, andcombined beam 852 may each be a free-space optical beam. Additionally,input-beam lens 820, filter 816, optical isolator 822, beam pick-off824, pump-laser lens 840, combiner 850, and focusing lens 854 may eachbe a free-space optical component. In particular embodiments, abooster-amplifier assembly 800 may be similar to a pre-amplifierassembly 700 or may include one or more optical components which aresimilar to those of a pre-amplifier assembly 700.

In particular embodiments, a booster-amplifier assembly 800 may includean output end 808 of a gain fiber 760. The gain fiber 760 may come fromanother amplifier assembly (e.g., another booster-amplifier assembly ora pre-amplifier assembly 700), and the output end 808 may be configuredto produce input beam 814 (e.g., input beam 814 is the output beam fromthe gain fiber 760 as well as the input beam to the booster-amplifierassembly 800). The input beam 814 may be a free-space beam that includeslight from a laser diode (e.g., seed laser diode 710 of pre-amplifierassembly 700) that is amplified while propagating through the gain fiber760.

In particular embodiments, a booster-amplifier assembly 800 may includean input-beam lens 820 (which may be referred as a collimating lens)configured to collect, collimate, or focus a free-space input beam 814from the gain fiber 760. The input beam 814 may be emitted from the gainfiber 760 into a diverging cone shape, and the input-beam lens 820 maycollect and collimate the input beam 814 to produce a collimatedfree-space optical beam. The input-beam lens 820 may include a singlespherical or aspheric lens. The input-beam lens 820 may be similar toseed-laser lens 720, pump-laser lens 740, or focusing lens 754 describedand illustrated herein.

In particular embodiments, a booster-amplifier assembly 800 may includea pump laser diode 830 configured to produce a free-space pump-laserbeam 834. The pump laser diode 830 in FIG. 18 may be similar to the pumplaser diode 730 in FIG. 15. The pump laser diode 830 may be any suitabletype of laser diode configured to produce light at a wavelength betweenapproximately 900 nm and approximately 1000 nm. The pump laser diode 830may include a laser-diode chip that directly emits a free-space opticalbeam (e.g., pump-laser beam 834) from a front facet of the pump laserdiode 830.

In particular embodiments, a booster-amplifier assembly 800 may includea pump-laser driver 838 configured to supply electrical current to apump laser diode 830. Additionally, the pump-laser driver 838 mayprovide temperature control for the pump laser diode 830. The pump-laserdriver 838 in FIG. 18 may be similar to the pump-laser driver 738described and illustrated herein. In particular embodiments, abooster-amplifier assembly 800 may include a pump-laser detector (notillustrated in FIG. 18), which may be similar to pump-laser detector 736described and illustrated herein. A pump-laser detector may beconfigured to receive light emitted from a back facet of the pump laserdiode 830 and provide an electrical signal corresponding to the receivedlight to the pump-laser driver 838.

In particular embodiments, a booster-amplifier assembly 800 may includea pump-laser lens 840 configured to collect, collimate, or focus afree-space pump-laser beam 834 emitted by pump laser diode 830. Thepump-laser lens 840, which may be similar to pump-laser lens 740described and illustrated herein, may include one or more sphericallenses, cylindrical lenses, aspheric lenses, GRIN lenses, or anysuitable combination thereof. As an example, the pump-laser lens 840 mayinclude a fast-axis collimating lens and a slow-axis collimating lens.

In particular embodiments, a booster-amplifier assembly 800 may includean optical filter 816 configured to remove ASE from the input beam 814.The input beam 814, when it exits the output end 808 of the gain fiber760, may include light that was amplified by the gain material of thegain fiber 760 as well as ASE produced by the gain material or residualpump light that was not absorbed by the gain material. The free-spaceoptical filter 816 may be a bandpass filter configured to transmit theamplified light over a particular wavelength range and reflect or absorblight outside that wavelength range. As an example, thebooster-amplifier assembly 800 may be configured to amplify light atapproximately 1550 nm, and the filter 816 may transmit light from 1548nm to 1552 nm. ASE light produced by the gain material in the gain fiber760 may have a spectrum that extends from approximately 1520 nm to 1600nm, and the filter 816 may remove most of the ASE from the input beam814 that is located outside the 1548-1552 nm wavelength range.Additionally, residual light from a pump laser may have a wavelength inthe 900-1000 nm range, and the filter 816 may remove most of theresidual pump light from the input beam 814. The filter 816 in FIG. 18may be similar to filter 630, 630A, or 630B described and illustratedherein.

In particular embodiments, a booster-amplifier assembly 800 may includean optical isolator 822. The optical isolator 822 in FIG. 18 may besimilar to the optical isolator 722 described and illustrated herein.The optical isolator 822 may be configured to transmit the input beam814 and prevent light from propagating back to the gain fiber 760.

In particular embodiments, a booster-amplifier assembly 800 may includea beam pick-off 824 and an input-beam detector 826 configured to detecta portion of input beam 814 reflected from the beam pick-off 824. A beampick-off 824 may be configured to transmit most of the input beam 814and reflect a small portion (e.g., ≤5%, ≤1%, or ≤0.1%) of the input beam814 to an input-beam detector 826. As an example, the beam pick-off 824may be a plate beam splitter that reflects approximately 0.5% ofincident light at approximately 1548-1552 nm (and transmitsapproximately 99.5% of the incident light). The input-beam detector 826may include a PN or PIN photodiode (e.g., an InGaAs PIN photodiode).

In particular embodiments, an input-beam detector 826 may be used tomonitor the power or energy of the input beam 814 or to monitor theperformance of the preceding amplifier stage (e.g., pre-amplifierassembly 700). As an example, a decrease in the power or energy of theinput beam 814 may indicate a problem with or a failure of thepre-amplifier assembly 700. Additionally, a decrease in the power orenergy of the input beam 814 may cause damage to the gain fiber 860 ordegradation in the performance of the booster-amplifier assembly 800.For example, if the input beam 814 does not have enough optical power toproperly seed or saturate the gain material in the gain fiber 860, thenthe gain fiber 860 may exhibit self-lasing or self-pulsing (which maydamage the gain fiber 860) or the amplified pulses produced at theoutput of the gain fiber 860 may include excessive amounts of opticalnoise. The input-beam detector 826 may be coupled to the pump-laserdriver 838, and if the power or energy of the input beam 814 decreasesbelow a particular threshold value, then the pump-laser driver 838 mayshut down or reduce the drive current supplied to the pump laser diode830 (e.g., to prevent damage to the multi-clad gain fiber 860 caused byhaving too little power in the input beam 814). Additionally oralternatively, the pump-laser driver 838 may send a notification (e.g.,to controller 150) indicating that there is a problem with the precedingamplifier stage.

In particular embodiments, a booster-amplifier assembly 800 may includea beam combiner 850 configured to combine the input beam 814 and thepump-laser beam 834 into a combined beam 852. The combiner 850 in FIG.18 may be similar to combiner 750 described and illustrated herein. Asan example, the combiner 850 may be a dichroic beam splitter cube orplate configured to reflect the input beam 814 (e.g., light atapproximately 1530-1560 nm) and transmit the pump-laser beam 834 (e.g.,light at approximately 920-980 nm) to produce the free-space combinedbeam 852. The input beam 814 and the pump-laser beam 834 may becollimated free-space beams, and the combined beam 852 may include theinput beam 814 and the pump-laser beam 834 overlapped so that they aresubstantially coaxial or coaligned.

In particular embodiments, a booster-amplifier assembly 800 may includea focusing lens 854 configured to focus a combined beam 852.Additionally, a booster-amplifier assembly 800 may include a multi-cladgain fiber 860 having an input end 868 configured to receive a focusedbeam. As an example, the focusing lens 854 may receive the combined beam852 from the combiner 850 and may focus the combined beam 852 onto aninput face 862 of the multi-clad gain fiber 860. The input face 862 ofthe multi-clad gain fiber 860 may be configured to receive a focusedbeam produced by the focusing lens 854. The focused beam may be coupledinto the multi-clad gain fiber 860 through the input face 862 and maythen propagate through the gain fiber 860. The light coupled into thegain fiber 860 may include light from the pump-laser beam 834 and lightfrom the input beam 814. The focusing lens 854 in FIG. 18 may be similarto focusing lens 754 described and illustrated herein. The input face862 and input end 868 in FIG. 18 may be similar to input face 762 andinput end 768, respectively, described and illustrated herein.

In particular embodiments, the input face 862 may be a cleaved orpolished surface of the gain fiber 860. The input face 862 may becleaved or polished so that it is substantially normal to the combinedbeam 852, or the input face 862 may be cleaved or polished at an angleso that it is angled with respect to the combined beam 852. Inparticular embodiments, the input face 862 may include an AR coatinghaving a low optical reflectivity at a wavelength of the input beam 814nm or the pump laser 830. As an example, the input face 862 may becleaved or polished, and then a dielectric coating may be deposited ontothe surface of the input face 862. The dielectric coating may be an ARcoating with a low optical reflectivity (e.g., R<1%) at the input-beamwavelength (e.g., 1545-1555 nm) or at the pump-laser wavelength (e.g.,940-980 nm). In particular embodiments, the input end 868 of gain fiber860 may be lensed. For example, the input face 862 may be shaped,tapered, or rounded to act as a lens so that the combined beam 852 isreceived and focused into the gain fiber 860.

In particular embodiments, a booster-amplifier assembly 800 may includea multi-clad gain fiber 860 having an input end 868, an input face 862,a core 864, an inner cladding 866, and an outer cladding 867. The inputend 868 of the gain fiber 860 may refer to a length of the end of thegain fiber 860 that is part of, attached to, located above, or containedwithin a platform 805 of the booster-amplifier assembly 800. As anexample, the gain fiber 860 may include a 2-6 meter length of opticalfiber, and a 1-100 mm end portion of the gain fiber 860 may be attachedto the platform 805 and may be referred to as the input end 868 of thegain fiber 860. The input end 868 of the gain fiber 860 may be attachedto or located on or above the platform 805, and the remaining length ofthe gain fiber 860 may be located outside of or beyond the boundaries ofthe platform 805.

In particular embodiments, a booster-amplifier assembly 800 may includea multi-clad gain fiber 860 that includes two or more cladding layers.In particular embodiments, a booster-amplifier assembly 800 may includea dual-clad gain fiber (which may be referred to as double-clad fiber ordouble-clad gain fiber) having a core 864, an inner cladding 866, and anouter cladding 867. In the example of FIG. 18, the multi-clad gain fiber860 is a dual-clad gain fiber with two layers of cladding (innercladding 866 and outer cladding 867). The core 864, the inner cladding866, and the outer cladding 867 may each include or be made from a glassmaterial. As an example, the core 864 may include a silica glass dopedwith gain material, and the inner cladding 866 and outer cladding 867may each include a silica glass. Additionally, the core 864, the innercladding 866, or the outer cladding 867 may be doped with a material tochange the refractive index. As an example, the outer cladding 867 maybe a silica glass doped with fluorine to decrease the refractive indexof the glass. As another example, the core 864 or inner cladding 866 maybe a silica glass doped with germanium to increase the refractive indexof the glass. In particular embodiments, a booster-amplifier assembly800 may include a triple-clad gain fiber having a core and threecladding layers. The core and the three cladding layers may each includeor be made from a glass material (e.g., silica, which may be doped witha material to change the refractive index). Rather than having one ormore cladding layers which are made from a polymer material (e.g.,acrylate or fluoroacrylate), a multi-clad gain fiber 860 may have anall-glass design where the core is made from glass doped with a gainmaterial, and the two or more cladding layers are each made from a glassmaterial. A gain fiber that includes a cladding made from polymer may besusceptible to degradation associated with exposure to elevatedtemperatures (e.g., the degradation may cause unwanted absorption ofpump light in the polymer region of the gain fiber). An all-glassmulti-clad gain fiber 860 may be able to operate for thousands of hourswithout experiencing significant performance degradation associated withelevated temperatures.

In particular embodiments, a multi-clad gain fiber 860 may include ajacket or outer layer of protective material configured to providemechanical protection for the core and cladding layers. As an example,the outermost cladding layer of a multi-clad gain fiber 860 may becoated with a polymer material which provides mechanical protection butis not configured to transmit or guide the light that propagates throughthe gain fiber 860.

In the example of FIG. 18, the combined beam 852 includes the input beam814 and the pump-laser beam 834. The light from the input beam 814 thatis coupled into the multi-clad gain fiber 860 is guided (as asingle-mode or multi-mode beam) by the core 864, and the light from thepump-laser beam 834 is guided (as a multi-mode beam) by the innercladding 866. For example, the inner cladding 866 may have a lowerrefractive index than the core 864, which provides index guiding so thelight from the input beam 814 is confined to propagate primarily in thecore 864. Similarly, the outer cladding 867 may have a lower refractiveindex than the inner cladding 866, so that the light from the pump-laserbeam 834 is confined to propagate primarily in the inner cladding 866and core 864. The core 864 or a portion of the inner cladding 866 aroundthe core may be doped with gain material (e.g., rare-earth dopants)which absorbs the pump-laser light and provides gain for the input-beamlight.

In particular embodiments, a free-space amplifier assembly with amulti-clad gain fiber 860 may allow for the optimization of beamparameters (e.g., beam size, divergence, focusing, or numerical aperture(NA)) of a pump-laser beam 834. Since a free-space amplifier assemblyuses a free-space combiner 850 (rather than a fiber-based combiner, suchas pump WDM 650), the parameters of the pump-laser beam 834 are notconstrained by having to send the pump light through a fiber-basedcombiner. As a result, the beam parameters of the pump-laser beam 834may be designed to optimize or maximize the coupling of the pump-laserbeam 834 into the multi-clad gain fiber 860. For example, in thebooster-amplifier assembly of FIG. 18, the focal length or location ofthe pump-laser lens 840 or the focusing lens 854 may be selected so thatthe focused pump-laser beam 834 that is incident on the input face 862has an NA that substantially matches the NA associated with the innercladding 866.

In particular embodiments, a booster-amplifier assembly 800 may includea platform 805 (which may be referred to as a mounting platform, amicro-bench, an optical bench, a micro-optical bench, or a siliconoptical bench), where one or more optical components are mechanicallyattached to the platform 805. In the example of FIG. 18, one or more ofthe following free-space optical components may be mechanically attachedto the platform 805: output end 808 of gain fiber 760, input-beam lens820, pump laser diode 830, pump-laser lens 840, beam combiner 850,focusing lens 854, optical isolator 822, beam pick-off 824, input-beamdetector 826, and input end 868 of multi-clad gain fiber 860.Additionally, an optical assembly (e.g., a combination of two or moreoptical components) may be attached to a platform 805. The platform 805in FIG. 18 may be similar to the platform 705 described and illustratedherein.

In particular embodiments, one or more optical components may bemechanically attached to a platform 805 by any suitable attachmenttechnique, such as for example, by bonding with an adhesive or epoxy,welding, brazing, soldering, mechanical fastening, or any suitablecombination thereof. In particular embodiments, one or more opticalcomponents may be directly or indirectly attached to a platform 805. Inparticular embodiments, a platform 805 may be made from or may includeany suitable material, such as for example, glass, a ceramic material, asemiconductor material, metal, carbon fiber, or any suitable combinationthereof. As an example, the material for a platform 805 may be selectedto have a relatively low CTE or a relatively high thermal conductivity.

In particular embodiments, an active-alignment technique or apassive-alignment technique may be used to position and attach anysuitable optical component to a platform 805. As an example, all theoptical components in a booster-amplifier assembly 800 may be activelyaligned, all the optical components may be passively aligned, or acombination of active and passive alignment techniques may be used inattaching optical components to a platform 805. As an example, thefocusing lens 854 may be actively aligned (e.g., positioned to maximizethe amount of input-beam light or pump-laser light that is coupled intothe gain fiber 860) and then attached to the platform 805. As anotherexample, the output end 808 of gain fiber 760 may be attached to theplatform 805 using a passive-alignment technique where a holder thatcontains the output end 808 is attached to the platform 805 based on oneor more registration features which are part of the platform 805.

In particular embodiments, a platform 805 may be contained within anenclosure that includes one or more feedthroughs for gain fiber 760 andmulti-clad gain fiber 860. As an example, the booster-amplifier assembly800 (including the platform 805 and the optical components attached tothe platform 705) may be installed into an enclosure that protects theoptical components from contaminants.

FIG. 19 illustrates an example light source 110 that includes afree-space pre-amplifier assembly 700 and a free-space booster-amplifierassembly 800. In particular embodiments, a pre-amplifier assembly 700 ora booster-amplifier assembly 800 may be part of a light source 110 of alidar system 100. As an example, a lidar system 100 may include ascanner 120, and a pre-amplifier assembly 700 or a booster-amplifierassembly 800 may provide amplified optical pulses to the scanner 120. InFIG. 19, the pre-amplifier assembly 700 sends seed-laser pulses andpump-laser light to the gain fiber 760. The gain fiber 760 amplifies theseed-laser pulses and sends the amplified pulses to thebooster-amplifier assembly 800. The booster-amplifier assembly 800combines the received pulses with pump-laser light and couples thecombined light into the gain fiber 860. The pulses of light are furtheramplified while traveling through the gain fiber 860. The gain fiber 860(or one or more optical components coupled to an output end of the gainfiber 860, such as for example, a filter, isolator, or a cladding powerstripper) may be terminated at an output collimator 340 which produces acollimated free-space output beam 125. The free-space output beam 125includes amplified optical pulses which may be sent to a scanner 120. Inparticular embodiments, an output collimator 340 may include or may becombined with one or more other optical components, such as for example,a filter, an isolator, or a cladding power stripper. As an example, theoutput collimator 340 in FIG. 19 may be an isolator/collimator assemblythat includes an isolator together with a collimator.

In particular embodiments, a light source 110 of a lidar system 100 mayinclude one or more pre-amplifier assemblies 700 or one or morebooster-amplifier assemblies 800. In the example of FIG. 19, the lightsource 110 includes one pre-amplifier assembly 700 coupled to onebooster-amplifier assembly 800, and the gain fiber 860 from thebooster-amplifier assembly 800 is terminated at an output collimator 340which produces a free-space output beam 125. In particular embodiments,a light source 110 may include one pre-amplifier assembly 700 coupled totwo or more booster-amplifier assemblies 800. For example, a lightsource 110 may include three amplifier stages arranged in series: apre-amplifier assembly 700 which is coupled to a first booster-amplifierassembly 800, which in turn is coupled to a second booster-amplifierassembly 800. The second booster-amplifier assembly 800 may beterminated at an output collimator 340 which produces a free-spaceoutput beam 125.

In particular embodiments, a free-space output beam 125 produced by abooster-amplifier assembly 800 may have one or more of the followingoptical characteristics: a wavelength between approximately 1400 nm andapproximately 1600 nm; a pulse duration less than or equal to 100nanoseconds; a duty cycle less than or equal to 10%; a pulse energygreater than or equal to 100 nanojoules; and a peak power greater thanor equal to 100 watts. As an example, the optical pulses from the gainfiber 760 supplied to the booster-amplifier assembly 800 may have apulse duration of approximately 4 ns, a pulse repetition frequency ofapproximately 600 kHz, and a pulse energy of approximately 0.1 μJ. Thebooster-amplifier assembly may further amplify the pulses to produceoptical pulses in the free-space output beam 125 having a pulse durationof approximately 4 ns, a pulse repetition frequency of approximately 600kHz, and a pulse energy of approximately 4 μJ (corresponding to a peakpower of approximately 1,000 watts).

In particular embodiments, a pre-amplifier assembly 700 may include oneor more optical components which are located remotely from or which arenot attached to platform 705. Similarly, a booster-amplifier assembly800 may include one or more optical components which are locatedremotely from or which are not attached to platform 805. As an example,seed laser diode 710 may not be attached to platform 705, and the lightfrom seed laser diode 710 may be delivered to the platform 705 by anoptical fiber. An end of the optical fiber may be attached to theplatform 705, and the seed-laser lens 720 may be used to collect andcollimate the seed-laser light emitted from the output face of theoptical fiber. As another example, pump laser diode 730 may not beattached to platform 705, and the pump-laser light may be delivered tothe platform 705 by optical fiber. An end of the optical fiber may beattached to the platform 705, and the pump-laser lens 740 may collectand collimate the pump-laser light emitted from the output face of theoptical fiber. As another example, pump laser diode 830 may not beattached to platform 805, and the pump-laser light may be delivered tothe platform 805 by optical fiber.

In particular embodiments, a pre-amplifier assembly 700 or abooster-amplifier assembly 800 may include a pump laser diode thatproduces pump light that co-propagates with input light that isamplified by the amplifier assembly. In the example of FIG. 15, lightfrom pump laser diode 730 co-propagates along the gain fiber 760 withlight from the seed laser diode 710 (e.g., the pump light propagatesthrough the gain fiber 760 in the same direction as the seed-laserlight). Similarly, in the example of FIG. 18, light from the pump laserdiode 830 co-propagates along the gain fiber 860 with the light frominput beam 814. In particular embodiments, a pre-amplifier assembly 700or a booster-amplifier assembly 800 may include a pump laser diode thatproduces pump light that counter-propagates with respect to input lightthat is amplified by the amplifier assembly. As an example, apre-amplifier assembly 700 may include a seed laser diode 710, aseed-laser lens 720, an optical isolator 722, a focusing lens 754, or aninput end 768 of a gain fiber 760. The pre-amplifier assembly 700 maynot include a pump laser diode 730, pump-laser lens 740, or combiner750. The pump laser diode 730 may be located at an output end 808 of thegain fiber 760, and light from the pump laser diode 730 may be coupledinto the output end 808 and may counter-propagate with respect to theseed-laser light (e.g., the pump light propagates in the oppositedirection of the seed-laser light). As another example, abooster-amplifier assembly 800 may not include a pump laser diode 830,pump-laser lens 840, or combiner 850. The pump laser diode 830 may belocated at an output end of the gain fiber 860, and light from the pumplaser diode 830 may counter-propagate with respect to light from theinput beam 814.

In particular embodiments, a pump laser diode for an amplifier assemblywith counter-propagating pump light may be located at a subsequentamplifier assembly. As an example, a pre-amplifier assembly 700 may notinclude a pump laser diode 730 attached to a platform 705 of thepre-amplifier assembly. The pump laser diode 730 and pump-laser lens 740may be attached to a platform 805 of a subsequent amplifier assembly(e.g., booster-amplifier assembly 800) that the output end 808 of gainfiber 760 is connected to, and light from the pump laser diode 730 maybe coupled into the output end of the gain fiber 760. As an example, acombiner (similar to combiner 750 or combiner 850) may be configured totransmit the input beam 814 and reflect light from the pump laser diode730. The pump-laser beam 734 may be reflected toward the output end 808,and the input-beam lens 820 may be configured to focus the pump-laserbeam 734 into the gain fiber 760.

In particular embodiments, a pre-amplifier assembly 700 or abooster-amplifier assembly 800 may include a semiconductor opticalamplifier (SOA). As an example, rather than using a gain fiber pumped bya pump laser diode, a free-space pre-amplifier assembly 700 may includea SOA configured to amplify light produced by a seed laser diode 710. ASOA may refer to an optical amplifier that uses a semiconductor deviceto provide an optical gain medium, and a SOA may be electrically pumpedby supplying electrical current to the SOA. A SOA may have a structurethat is similar to a laser diode and may include one or moresemiconductor materials (e.g., InP, InGaAs, InGaAsP, or InAlGaAs)configured to act as an optical waveguide and provide optical gain. Thewaveguide may extend from a front facet to a back facet of a SOA and mayguide light that is coupled into and amplified by the SOA. Whenelectrical current is supplied to a SOA, the SOA may provide opticalgain for input light that propagates along the SOA waveguide. Forexample, light from a seed laser (e.g., light at 1500-1600 nmwavelength) may be coupled into a SOA through a front facet, and thelight may be amplified as it propagates from the front facet to the backfacet.

In particular embodiments, the front facet or back facet of a SOA mayinclude an AR coating to reduce the reflectivity of the facet so thatthe SOA acts as an optical amplifier rather than a laser. The waveguideof a SOA may be tilted or angled with respect to the front or back facetto further reduce the reflectivity of light at the facets (e.g., lightpropagating along the waveguide within a SOA that is reflected at afacet may not be coupled back into the waveguide due to the angledwaveguide). In particular embodiments, the waveguide of a SOA may have aflared or tapered structure where the size of the waveguide increasestowards the back facet of the SOA. The increase in waveguide sizedecreases the power density of the amplified light at the back facetwhich reduces the possibility of causing optical damage to the backfacet. In particular embodiments, a SOA may have a length (e.g., adistance between the front and back facets) between approximately 100 μmand approximately 10 mm.

In particular embodiments, the electrical drive current supplied to aSOA may include DC current or pulsed current. As an example, a seedlaser may produce optical pulses that are coupled into a SOA. Thecurrent supplied to the SOA may be a substantially constant DC current,or the current supplied to the SOA may be pulsed at a pulse frequencythat matches the pulse repetition frequency of the seed laser (e.g., theSOA current is pulsed so that optical gain is only provided when aseed-laser pulse is present). As another example, a seed laser mayproduce CW light (e.g., non-pulsed light with a substantially constantoutput power), and the current supplied to the SOA may be pulsed toproduce amplified optical pulses at the output of the SOA. When currentis supplied to the SOA, the CW light may be amplified by the SOA, andwhen little or no current is supplied to the SOA, there may be nooptical gain present, and the CW light may be absorbed by the SOA.

In particular embodiments, a free-space pre-amplifier assembly 700 witha SOA may include one or more of the following optical components: seedlaser diode 710, seed-laser detector 716, seed-laser driver 718,seed-laser lens 720, optical isolator 722, optical filter 816, focusinglens 754, a SOA, and an output lens (e.g., to collect, collimate, orfocus the amplified light produced by the SOA). For example, aseed-laser lens 720 may collect, collimate, or focus light emitted bythe seed laser diode 710, and a focusing lens (e.g., similar to focusinglens 754 in FIG. 15) may focus the light from the seed laser diode 710onto the front facet of a SOA. The light from the seed laser diode 710may then be coupled into the SOA and amplified as it propagates along awaveguide within the SOA. The amplified light emitted from the backfacet of the SOA may be received and collimated by an output lens toproduce a collimated free-space output beam. The output lens, which maybe similar to lens 820 in FIG. 18, may produce a collimated free-spacebeam that is sent to another amplifier stage (e.g., booster-amplifierassembly 800 illustrated in FIG. 18). A pre-amplifier assembly 700 witha SOA may include a filter (e.g., similar to filter 816 in FIG. 18)located after the SOA and configured to remove ASE from the output beam(e.g., ASE produced by the SOA). A pre-amplifier assembly 700 with a SOAmay not include a pump laser diode, pump-laser lens, pump-laserdetector, combiner, or gain fiber.

In particular embodiments, a pre-amplifier assembly 700 with a SOA mayinclude one or more of the following optical components mechanicallyattached to a platform 705: a SOA, seed laser diode 710, seed-laser lens720, optical isolator 722, filter 816, focusing lens 754, and an outputlens. As an example, a light source 110 of a lidar system 100 mayinclude a seed laser diode 710 that produces a free-space beam and aseed-laser lens 720 that collimates the seed-laser beam. The lightsource 110 may also include a focusing lens 754 that focuses theseed-laser beam into the waveguide of a SOA. In particular embodiments,a booster-amplifier assembly 800 may include a pre-amplifier assembly700 with a SOA. As an example, a seed laser diode 710, seed-laser lens720, focusing lens 754, or a SOA may be attached to a platform 805 of abooster-amplifier assembly 800. The amplified pulses emitted from theback facet of the SOA may be collimated by an input-beam lens 820 toproduce a free-space input beam 814. The input beam 814 may be combinedwith light from a pump laser diode 830, and the combined beam 852 may becoupled into a gain fiber (e.g., similar to gain fiber 760 in FIG. 15 orgain fiber 860 in FIG. 18).

FIG. 20 illustrates an example fiber-optic amplifier 470 with two pumplaser diodes (pump laser 1 and pump laser 2). The fiber-optic amplifier470 illustrated in FIG. 20 may be part of a light source 110 of a lidarsystem 100. The fiber-optic amplifier 470 illustrated in FIG. 20 may besimilar to the fiber-optic amplifier 470 illustrated in FIG. 13 or mayinclude one or more fiber-optic components similar to those of amplifier470 illustrated in FIG. 11, FIG. 13, or FIG. 14. As an example, filter630A, coupler 600A, photodiode 610A, isolator 620A, or gain fiber 660illustrated in FIG. 20 may be similar to the corresponding opticalcomponents in FIG. 13. Additionally, isolator 620B, coupler 600B,photodiode 610B, or filter 630B illustrated in FIG. 20 may be similar tothe corresponding optical components in FIG. 13. The amplifier 470 inFIG. 20 may be a booster amplifier or a power amplifier, and the gainfiber 660 in FIG. 20 may be multi-clad gain fiber (e.g., similar tomulti-clad gain fiber 860 in FIG. 18). The output of amplifier 470 inFIG. 20 may be coupled to another amplifier or may be coupled to anoutput collimator that produces a free-space output beam.

In particular embodiments, light from two or more pump lasers in afiber-optic amplifier 470 may be combined together with input lightusing a pump WDM 650. In FIG. 20, after passing through the filter 630A,coupler 600A, and isolator 620A, the input light is combined with lightfrom pump laser 1 and pump laser 2 by pump WDM 650. A pump WDM 650 mayinclude a (N+1)×1 fiber-optic combiner which combines light from N pumplasers with an input signal and sends the combined pump-signal light toan output port (e.g., a fiber-optic cable that may be spliced to gainfiber 660). A (N+1)×1 fiber-optic combiner is a (N+2)-port fiber-opticdevice with N pump-input ports for N respective pump lasers, onesignal-input port, and one output port. As an example, a (2+1)×1combiner is a four-port device that combines input light (received at afirst port) with light from two pump lasers (received at second andthird ports, respectively), and sends the combined light out a fourthport (which may be coupled or spliced to gain fiber 660). As anotherexample, a fiber-optic amplifier 470 may include three or four pumplasers which are combined with input light by a (3+1)×1 combiner or a(4+1)×1 combiner, respectively.

The pump WDM 650 in FIG. 20 is a (2+1)×1 combiner which combines lightfrom the two pump lasers with the input light and sends the combinedlight to the gain fiber 660. Pump laser 1 and pump laser 2 may eachpropagate to the pump WDM 650 via a multi-mode fiber-optic cable, andthe input signal may propagate along a single-mode fiber-optic cable.The output fiber-optic cable from a pump WDM 650 may be a multi-cladfiber where the input light propagates primarily along the core, and thepump light propagates primarily in a cladding layer. As an example, theoutput fiber-optic cable from a pump WDM 650 may be a double-clad fiberwhich is spliced to a double-clad gain fiber.

In particular embodiments, a fiber-optic amplifier 470 may include twoor more pump lasers, and light from the two or more pump lasers may beco-propagating or counter-propagating with respect to input light thatis amplified by the amplifier 470. As an example, a pump WDM 650 may belocated at an output end of gain fiber 660, and light from two or morepump lasers may counter-propagate along the gain fiber 660 with respectto the input light. In FIG. 20, light from the two pump lasers (pumplaser 1 and pump laser 2) co-propagates along the gain fiber 660 withthe input light. In particular embodiments, a fiber-optic amplifier 470may include one or more co-propagating pump lasers and one or morecounter-propagating pump lasers. The fiber-optic amplifier in FIG. 13includes a co-propagating pump laser 640A and a WDM 650A located at aninput end of gain fiber 660 and a counter-propagating pump laser 640Band a WDM 650B located at an output end of gain fiber 660. If pump laser640A and pump laser 640B operate at different wavelengths, then aspectral filter may be used to prevent residual or back-reflected lightfrom one pump laser from damaging or destabilizing the other pump laser.For example, if pump laser 640A operates at 920 nm and pump laser 640Boperates at 950 nm, then the light from pump laser 640A may betransmitted through a filter that transmits 920-nm light and blocks theresidual 950-nm light from pump laser 640B. Similarly, the light frompump laser 640B may be transmitted through a filter that transmits950-nm light and blocks 920-nm light.

FIG. 21 illustrates an example fiber-optic booster amplifier 470 withtwo pump laser diodes (pump laser 1 and pump laser 2). The boosteramplifier 470 in FIG. 21 may be part of a light source 110 of a lidarsystem 100, and the output beam 125 may be sent to a scanner 120 of thelidar system 100. The booster amplifier 470 illustrated in FIG. 21 maybe similar to the booster amplifier 470 illustrated in FIG. 14 or mayinclude one or more fiber-optic components similar to those of amplifier470 illustrated in FIG. 11, FIG. 13, FIG. 14, or FIG. 20. As an example,isolator 620A, gain fiber 660, or isolator 620B in FIG. 21 may besimilar to the corresponding optical components in FIG. 13 or FIG. 20.The cladding power stripper 680 or collimator 340 in FIG. 21 may besimilar to the corresponding optical components in FIG. 14. The pump WDM650 in FIG. 21 may be a (2+1)×1 fiber-optic combiner similar to the pumpWDM 650 in FIG. 20.

In FIG. 20 or FIG. 21, the input light may include optical pulsesreceived from a previous amplifier stage or from a seed laser. As anexample, the input light may include pulses of light having a wavelengthbetween approximately 1400 nanometers and approximately 1600 nanometers,a pulse duration less than or equal to 100 nanoseconds, or a duty cycleless than or equal to 10%. In FIG. 21, the amplifier 470 is terminatedat output collimator 340, and the output collimator 340 may produce afree-space output beam 125 that includes amplified optical pulses. Pumplaser 1 or pump laser 2 in FIG. 20 or FIG. 21 may each be similar topump laser 640 in FIG. 11 or FIG. 14 or may be similar to pump laser640A or 640B in FIG. 13. As an example, pump laser 1 and pump laser 2may each be a fiber-coupled laser diode with an operating wavelengthbetween approximately 900 nm and 1000 nm. Additionally, pump laser 1 andpump laser 2 may each be configured to produce any suitable amount ofaverage optical pump power, such as for example, approximately 100 mW,500 mW, 1 W, 2 W, 5 W, 10 W, 15 W, or 20 W of pump power.

FIG. 22 illustrates a top view of an example free-space amplifierassembly 900 with two pump laser diodes (pump laser 1 and pump laser 2).The free-space amplifier assembly 900 in FIG. 22 may be part of a lightsource 110 of a lidar system 100. In particular embodiments, afree-space amplifier assembly 900 may include two or more pump laserdiodes. The amplifier assembly 900 in FIG. 22 includes two pump laserdiodes which are combined with input beam 914, and then the combinedfree-space beam 952 is coupled into a multi-clad gain fiber 960. Themulti-clad gain fiber 960 may include gain material (e.g., rare-earthdopants) that absorbs the pump light from the two pump laser diodes andprovides optical gain for the light from input beam 914. The free-spaceamplifier assembly 900 illustrated in FIG. 22 may be similar to thefree-space booster-amplifier assembly 800 in FIG. 18 or may include oneor more free-space optical components similar to those of amplifierassembly 700 in FIG. 15 or amplifier assembly 800 in FIG. 18. Inparticular embodiments, the fiber-optic amplifier 470 in FIG. 20 or FIG.21 or the free-space amplifier assembly 900 in FIG. 22 may each bereferred to as an optical amplifier with multi-wavelength pumping or anoptical amplifier with multiple pump lasers.

The free-space input beam 914 in FIG. 22 may include pulses of lighthaving one or more wavelengths between approximately 1400 nm andapproximately 1600 nm, a pulse duration less than or equal to 100nanoseconds, or a duty cycle less than or equal to 10%. In particularembodiments, free-space input beam 914 may be supplied to amplifierassembly 900 by a seed laser diode or by a gain fiber from a previousamplifier stage. As an example, an amplifier assembly 900 may include afree-space seed laser diode (e.g., similar to seed laser diode 710 inFIG. 15) configured to supply the free-space input beam 914. Theamplifier assembly 900 may also include a lens (e.g., similar toseed-laser lens 720 in FIG. 15) configured to collimate or focus theinput beam 914. As another example, an amplifier assembly 900 mayinclude a fiber-coupled seed laser diode (e.g., similar to laser diode440 in FIG. 8). An output end of a fiber-optic cable from thefiber-coupled seed laser diode may be attached to the platform 905 andmay supply the free-space input beam 914. As another example, the outputend of a gain fiber (e.g., similar to output end 808 of gain fiber 760in FIG. 18) may be attached to the platform 905 and may supply thefree-space input beam 914. The amplifier assembly 900 may also include alens (similar to input-beam lens 820 in FIG. 18) configured to collimateor focus the input beam 914.

Pump laser 1 or pump laser 2 in FIG. 22 may each be similar to pumplaser diode 730 in FIG. 15 or pump laser diode 830 in FIG. 18. As anexample, pump laser 1 and pump laser 2 may each be a free-space pumplaser diode with an operating wavelength between approximately 900 nmand 1000 nm. Additionally, pump laser 1 and pump laser 2 may beconfigured to produce free-space pump-laser beam 934A and free-spacepump-laser beam 934B, respectively, each beam having any suitable amountof average optical pump power, such as for example, approximately 100mW, 500 mW, 1 W, 2 W, 5 W, 10 W, 15 W, or 20 W of pump power. In FIG.22, pump-laser lens 940A (which is configured to collimate or focus thelight emitted by pump laser 1) and pump-laser lens 940B (which isconfigured to collimate or focus the light emitted by pump laser 2) mayeach be similar to pump-laser lens 740 in FIG. 15 or pump-laser lens 840in FIG. 18.

In particular embodiments, an amplifier assembly 900 may include one ormore pump-laser drivers (which may be similar to pump-laser driver 738in FIG. 15 or pump-laser driver 838 in FIG. 18). In FIG. 22, pump-laserdriver 938A supplies drive current to pump laser 1, and pump-laserdriver 938B supplies drive current to pump laser 2. In particularembodiments, an amplifier assembly 900 may include one or morepump-laser detectors (which may be similar to pump-laser detector 736 inFIG. 15). In FIG. 22, pump laser 1 may emit pump-laser back-facet light932A which may be detected by a pump-laser detector 936A, and thepump-laser detector 936A may send an electrical signal corresponding tothe detected light to pump-laser driver 938A. Similarly, pump laser 2may emit pump-laser back-facet light 932B which may be detected by apump-laser detector 936B, and the pump-laser detector 936B may send anelectrical signal corresponding to the detected light to pump-laserdriver 938B.

In particular embodiments, an amplifier assembly 900 may include two ormore beam combiners (which may be similar to combiner 750 in FIG. 15 orcombiner 850 in FIG. 18). In FIG. 22, combiner 950A combines the inputbeam 914 with the pump-laser beam 934A to produce an intermediate beam951. The input beam 914 and the pump-laser beam 934A may be collimatedfree-space beams, and the intermediate beam 951 may include the inputbeam 914 and the pump-laser beam 934A overlapped so that they aresubstantially coaxial or coaligned. In FIG. 22, combiner 950B combinesthe intermediate beam 951 with the pump-laser beam 934B to produce thecombined free-space beam 952. The combined beam 952 may include threefree-space beams (input beam 914, pump-laser beam 934A, and pump-laserbeam 934B) overlapped so that they are substantially coaxial orcoaligned. The combined beam 952 is focused into the multi-clad gainfiber 960 by the focusing lens 954.

In particular embodiments, combiner 950A or combiner 950B may each be adichroic beam splitter cube or a dichroic beam splitter plate. As anexample, combiner 950A may be a dichroic beam splitter cube configuredto transmit the input beam 914 (e.g., light with a 1500-1600 nmwavelength) and reflect the pump-laser beam 934A (e.g., light with a900-1000 nm wavelength). As another example, combiner 950B may be adichroic beam splitter cube configured to transmit the pump-laser beam934B and reflect the intermediate beam 951. For example, if input beam914 has a wavelength of 1540-1560 nm, pump-laser beam 934A has awavelength of 940-990 nm, and pump-laser beam 934B has a wavelength of900-940 nm, then combiner 950B may transmit light at 900-940 nm and mayreflect light at 940-990 nm and 1540-1560 nm.

In particular embodiments, combiner 950A or combiner 950B may each beconfigured to reflect or transmit light at any suitable wavelength. Asan example, in FIG. 22, combiner 950A is configured to transmit theinput beam 914 (which may include light having a wavelength within the1500-1600 nm range) and reflect the pump-laser beam 934A (which mayinclude light have a wavelength within the 900-1000 nm range). Asanother example, combiner 950A may be configured to transmit thepump-laser beam 934A and reflect the input beam 914. As another example,combiner 950B may be configured to transmit the pump-laser beam 934B andreflect the intermediate beam 951 (as illustrated in FIG. 22), orcombiner 950B may be configured to transmit the intermediate beam 951and reflect the pump-laser beam 934B.

In particular embodiments, input beam 914, pump-laser beam 934A, andpump-laser beam 934B may have any suitable arrangement or may becombined in any suitable order. In the example of FIG. 22, the inputbeam 914 is first combined with the pump-laser beam 934A, and then theintermediate beam 951 (which includes the input beam 914 and thepump-laser beam 934A) is combined with the pump-laser beam 934B. Asanother example, pump-laser beams 934A and 934B may first be combinedtogether (e.g., using a combiner that transmits light at 900-940 nm andreflects light at 940-990 nm, or vice versa), and then the combinedpump-laser beams may be combined with input beam 914 (e.g., using acombiner that transmits light at 900-990 nm and reflects light at1540-1560 nm, or vice versa).

In particular embodiments, combiner 950A or combiner 950B may be apolarizing optical element (which may be referred to as a polarizationcombiner), such as for example, a polarizing beam splitter (PBS) cubeconfigured to combine two beams having orthogonal polarizations into asingle output beam. As an example, in FIG. 22, the input beam 914 may behorizontally polarized, and the pump-laser beam 934A may be verticallypolarized. Combiner 950A may be a PBS cube that transmits thehorizontally polarized input beam 914 and reflects the verticallypolarized pump-laser beam 934A. As another example, in FIG. 22, theinput beam 914 and the pump-laser beam 934A may both be verticallypolarized, and the pump-laser beam 934B may be horizontally polarized.Combiner 950A may be a dichroic beam splitter cube, and combiner 950Bmay be a PBS cube that reflects the vertically polarized input beam 914and pump-laser beam 934A and transmits the horizontally polarizedpump-laser beam 934B. As another example, if pump-laser beams 934A and934B are first combined together, they may be combined together using aPBS cube. Pump laser diode 1 may be configured to produce a verticallypolarized pump-laser beam 934A, and pump laser diode 2 may be configuredto produce a horizontally polarized pump-laser beam 934B. For example,pump laser diode 2 may be mechanically mounted at 90 degrees withrespect to pump laser diode 1 so that the polarizations of pump-laserbeams 934A and 934B are orthogonal. As another example, pump-laser beam934B may be sent through a half-wave plate to rotate the polarization ofthe pump-laser beam 934B by 90 degrees with respect to pump-laser beam934A. A first combiner may be a polarization combiner (e.g., a PBS cube)that combines the two orthogonally polarized pump beams, and a secondcombiner may be a dichroic beam splitter cube that combines the two900-1000 nm pump beams with a 1500-1600 nm input beam 914 (e.g., thedichroic beam splitter may reflect light at 900-1000 nm and transmitlight at 1500-1600 nm, or vice versa). If the pump-laser beams 934A and934B are combined based on their orthogonal polarizations (and not basedon their different wavelengths, as with a dichroic beam splitter), thenthe pump laser diode 1 and pump laser diode 2 may operate atsubstantially the same wavelength (e.g., 940 nm±4 nm).

In particular embodiments, an amplifier assembly 900 may include amulti-clad gain fiber 960 (which may include a core 964, inner cladding966 nm, and outer cladding 967), and the input end 968 of the multi-cladgain fiber 960 may be attached to platform 905. The multi-clad gainfiber 960 illustrated in FIG. 22 may be similar to the multi-clad gainfiber 860 in FIG. 18. The multi-clad gain fiber 960 may be anerbium-doped gain fiber or an erbium/ytterbium-doped gain fiber. Themulti-clad gain fiber 960 may have an all-glass design where the core964 is made from glass doped with a gain material, and the innercladding 966 and outer cladding 967 are each made from a glass material(e.g., silica glass doped with a material to alter the refractiveindex). The focusing lens 954 may focus the combined beam 952 onto theinput face 962 of the gain fiber 960, and the focused beam may becoupled into the gain fiber 960 through the input face 962. The lightfrom the input beam 914 that is coupled into the multi-clad gain fiber960 may be guided (as a single-mode or multi-mode beam) by the core 964,and the light from pump-laser beams 934A and 934B may be guided (asmulti-mode beams) by the inner cladding 966. The core 964 or a portionof the inner cladding 966 around the core may be doped with gainmaterial (e.g., rare-earth dopants) which absorbs the light from thepump-laser beams 934A and 934B and provides gain for the light from theinput beam 914.

In particular embodiments, amplifier assembly 900 may include one ormore optical components similar to optical isolator 722, opticalisolator 822, filter 816, or beam pick-off 824 and input-beam detector826, as described herein. As an example, input beam 914 may pass throughan optical isolator, filter, or a beam pick-off (which sends a portionof input beam 914 to an input-beam detector). As another example,pump-laser beam 934 or pump-laser beam 934B may pass through an opticalisolator or filter.

In particular embodiments, an amplifier assembly 800 may include aplatform 905 (which may be similar to platform 705 or platform 805described and illustrated herein) where one or more optical componentsare mechanically attached to the platform 905. In the example of FIG.22, one or more of the following free-space optical components may bemechanically attached to the platform 905: pump laser 1, pump laser 2,pump-laser lens 940A, pump laser lens 940B, combiner 950A, combiner950B, focusing lens 954, and the input end 968 of the multi-clad gainfiber 960. Additionally, any other suitable optical component (e.g., anisolator, filter, or beam pick-off) or an optical assembly (e.g., acombination of two or more optical components) may be attached to aplatform 905.

In particular embodiments, one or more optical components may bemechanically attached to a platform 905 by any suitable attachmenttechnique, such as for example, by bonding with an adhesive or epoxy,welding, brazing, soldering, mechanical fastening, or any suitablecombination thereof. In particular embodiments, one or more opticalcomponents may be directly or indirectly attached to a platform 905. Inparticular embodiments, an active-alignment technique or apassive-alignment technique may be used to position and attach anysuitable optical component to a platform 905. As an example, all theoptical components in an amplifier assembly 900 may be actively aligned,all the optical components may be passively aligned, or a combination ofactive and passive alignment techniques may be used in attaching opticalcomponents to a platform 905. In particular embodiments, a platform 905may be made from or may include any suitable material, such as forexample, glass, a ceramic material, a semiconductor material, metal,carbon fiber, or any suitable combination thereof. As an example, thematerial for a platform 905 may be selected to have a relatively low CTEor a relatively high thermal conductivity.

In particular embodiments, an amplifier assembly may include two or morepump lasers. As an example, a fiber-optic amplifier with multiple pumplasers (e.g., similar to amplifier 470 in FIG. 20 or FIG. 21) mayinclude three pump lasers which are combined with input light by a(3+1)×1 combiner. Each pump laser may have approximately the sameoperating wavelength, or two or more of the pump lasers may havedifferent operating wavelengths. As another example, a free-spaceamplifier with multiple pump lasers (e.g., similar to amplifier assembly900 in FIG. 22) may include three pump lasers which are combined with aninput beam 914 using three combiners (similar to combiner 950A or 950Bin FIG. 22). In particular embodiments, an amplifier that includes twoor more pump lasers may provide higher pump power to a gain fiber (ascompared to an amplifier with a single pump laser), may provideredundant pump-laser sources in case one of the pump lasers fails, ormay allow the pump lasers to operate at lower power levels (which mayextend the lifetime of the pump lasers).

In particular embodiments, a free-space amplifier assembly 900 mayinclude two or more pump lasers that produce co-propagating orcounter-propagating pump light. As an example, pump laser 1 and pumplaser 2 may be configured as counter-propagating pump lasers. A platform905 of amplifier assembly 900 may include a focusing lens and an inputend 968 of gain fiber 960. For example, a seed laser diode 710 and a SOAmay be attached to platform 905 of amplifier assembly 900 and may beconfigured to produce input beam 914 which is focused into the input end968 of gain fiber 960 by a focusing lens 954. Pump laser 1, pump-laserlens 940A, combiner 950A, pump laser 2, pump-laser lens 940B, orcombiner 950B may be located at an output end of gain fiber 960. Pumplaser 1 and pump laser 2 may be located at an output end of gain fiber960, and the light from pump laser 1 and pump laser 2 maycounter-propagate with respect to the light from input beam 914 thatpropagates along the gain fiber 960. In the example of FIG. 22, pumplaser 1 and pump laser 2 are configured to co-propagate with the lightfrom input beam 914. In particular embodiments, a free-space amplifierassembly 900 with multiple pump lasers may include one or moreco-propagating pump lasers and one or more counter-propagating pumplasers. For example, pump laser 1, pump-laser lens 940A, and combiner950A may be attached to platform 905 along with the input end 968 ofgain fiber 960, and pump laser 2, pump-laser lens 940B, and combiner950B may be located at an output end of gain fiber 960. In particularembodiments, if pump laser 1 and pump laser 2 operate at differentwavelengths, then a spectral filter may be used to prevent residual orback-reflected light from one pump laser from damaging or destabilizingthe other pump laser. For example, if pump laser 1 operates at 920 nmand pump laser 2 operates at 950 nm, then the light from pump laser 1may be transmitted through a filter that transmits 920-nm light andblocks the residual 950-nm light from pump laser 2. Similarly, the lightfrom pump laser 2 may be transmitted through a filter that transmits950-nm light and blocks 920-nm light.

FIG. 23 illustrates an example absorption spectrum for anerbium/ytterbium gain fiber. The absorption spectrum represents thewavelength dependence of the absorption of pump light, in units of dBper meter of erbium/ytterbium gain fiber. For example, light from a925-nm pump laser may experience an absorption of approximately 2.5 dB/mwhile propagating through a gain fiber (e.g., gain fiber 660, gain fiber760, gain fiber 860, or gain fiber 960), and light from a 976-nm pumplaser may experience an absorption of approximately 17 dB/m. As anotherexample, light from a pump laser with a 940-nm operating wavelength mayexperience an absorption of approximately 3 dB/m, and for a 3.33-meterlength of gain fiber, the total absorption at 940 nm is approximately 10dB (e.g., approximately 90% of the pump light is absorbed whilepropagating through a 3.33-meter gain fiber). The absorption spectrum inFIG. 23 has a relatively small absorption peak around 915 nm, arelatively large absorption peak around 976 nm, and a region between 920nm and 970 nm with some moderate variation in absorption.

In particular embodiments, a gain fiber with an absorption that varieswith wavelength (e.g., an absorption spectrum similar to thatillustrated in FIG. 23) may be configured to receive pump light from twoor more pump lasers (e.g., pump laser 1 and pump laser 2 illustrated inFIG. 20, FIG. 21, or FIG. 22) and provide optical gain for an opticalsignal propagating through the gain fiber. The pump lasers may eachproduce pump light with a wavelength between approximately 900 nm andapproximately 1000 nm, and the optical signal that is amplified may havea wavelength between approximately 1400 nm and approximately 1600 nm. InFIG. 23, pump laser 1 has an operating wavelength of approximately 920nm, and pump laser 2 has an operating wavelength of approximately 950nm. The light from pump laser 1 and pump laser 2 may be combinedtogether, and the combined 920-nm/950-nm pump-laser light may be coupledinto a gain fiber to provide optical gain for a 1500-1600 nm opticalsignal (e.g., pulses of light at approximately 1550 nm).

In particular embodiments, an optical amplifier may include a first pumplaser diode configured to produce pump light having a first amount ofoptical power at a first wavelength and a second pump laser diodeconfigured to produce pump light having a second amount of optical powerat a second wavelength. The two pump lasers may operate at differentwavelengths or may operate at approximately the same wavelength. Inparticular embodiments, two pump lasers which operate at differentwavelengths may refer to two pump lasers having operating wavelengths ata particular operating temperature (e.g., 25° C.) that differ by greaterthan or equal to any suitable amount, such as for example, 5 nm, 10 nm,20 nm, 30 nm, 40 nm, 50 nm, or 80 nm. As an example, two pump lasershaving different wavelengths may refer to pump laser 1 producing 930-nmlight at a 25° C. operating temperature and pump laser 2 producing940-nm light at 25° C. (which corresponds to a 10-nm wavelengthdifference). As the temperature changes, the wavelengths of the two pumplasers may shift, and the wavelength difference between the pump-laserwavelengths may remain approximately constant. As an example, at 25° C.,pump laser 1 may produce light at 920 nm, and pump laser 2 may producelight at 940 nm (corresponding to a 20-nm wavelength difference). If thetemperature changes to 70° C., the wavelength of pump laser 1 may shiftto approximately 935 nm, and the wavelength of pump laser 2 may shift toapproximately 955 nm (which still corresponds to a 20-nm wavelengthdifference). In particular embodiments, two pump lasers which operate atthe same wavelength may refer to two pump lasers having operatingwavelengths at a particular operating temperature that differ by lessthan or equal to any suitable amount (e.g., less than or equal to 1 nm,2 nm, 4 nm, or 8 nm). As an example, two pump lasers havingapproximately the same operating wavelength may refer to each pump laserproducing light between approximately 938 nm and approximately 942 nmwhen operating at a particular temperature (e.g., 25° C.).

In particular embodiments, the operating wavelengths of the pump lasersin an optical amplifier with multiple pump lasers may be approximatelythe same. As an example, in FIG. 20, FIG. 21, or FIG. 22, pump laser 1and pump laser 2 may operate at approximately the same wavelength (e.g.,940 nm±2 nm). In particular embodiments, the operating wavelengths ofthe pump lasers in an optical amplifier with multiple pump lasers may bedifferent. As an example, in FIG. 20, FIG. 21, or FIG. 22, pump laser 1and pump laser 2 may operate at different wavelengths. For example, pumplaser 1 may produce pump light at a wavelength between approximately 900nm and approximately 940 nm, and pump laser 2 may produce pump lightbetween approximately 940 nm and approximately 990 nm. As anotherexample, pump laser 1 may produce light at approximately 920 nm, andpump laser 2 may produce light at approximately 950 nm (as illustratedin FIG. 23). In particular embodiments, two or more pump lasers in anoptical amplifier may operate in two or more corresponding wavelengthranges which may be non-overlapping or overlapping. As an example, pumplaser 1 may operate in a 900 nm to 940 nm wavelength range, and pumplaser 2 may operate in a non-overlapping wavelength range of 940 nm to990 nm. As the temperature of pump laser 1 changes, the operatingwavelength of pump laser 1 may shift within the 900-940 nm wavelengthrange. Similarly, as the temperature of pump laser 2 changes, theoperating wavelength of pump laser 2 may shift within the 940-900 nmwavelength range. As another example, pump laser 1 may operate in a 900nm to 950 nm wavelength range, and pump laser 2 may operate in anoverlapping wavelength range of 940 nm to 990 nm. As the temperaturechanges, the wavelength of pump laser 1 may shift within the 900-950 nmwavelength range, and the wavelength of pump laser 2 may shift withinthe 940-990 nm wavelength range.

In particular embodiments, an optical amplifier, a light source 110, ora lidar system 100 may include a controller configured to adjust theamount of optical power produced by pump laser 1 and pump laser 2.Adjusting the amount of optical power produced by a pump laser mayinclude adjusting the electrical current supplied to the pump laser. Asan example, lidar system 100 may include a controller 150 which maycontrol the amount of electrical current supplied to pump laser 1 andpump laser 2. In FIG. 22, a controller may be coupled to pump-laserdriver 938A and may send an electrical signal to the pump-laser driver938A to set or adjust the electrical current that is supplied to pumplaser 1. Similarly, a controller may be coupled to pump-laser driver938B and may send an electrical signal to the pump-laser driver 938B toset or adjust the electrical current that is supplied to pump laser 2.In particular embodiments, the output power of a pump laser may varywith the electrical current supplied to the pump laser. As an example,the output power and electrical current may be positively correlated sothat an increase in electrical current results in an increase in outputpower. For example, pump laser 1 may produce approximately 5 W of outputpower with a 7-amp electrical current, and pump laser 1 may produceapproximately 10 W of output power with a 12-amp electrical current.

In particular embodiments, the amount of optical power produced by pumplaser 1 or pump laser 2 may be adjusted to any suitable value betweenapproximately 0 watts and approximately 20 watts. As an example, theelectrical current supplied to pump laser 1 may be adjusted so that theamount of optical power produced by pump laser 1 may be varied between 0watts and any suitable maximum operating power, such as for example, amaximum operating power of approximately 1 W, 2 W, 5 W, 10 W, 15 W, or20 W. Similarly, the electrical current supplied to pump laser 2 may beadjusted so that the amount of optical power produced by pump laser 2may be varied between 0 watts and approximately 1 W, 2 W, 5 W, 10 W, 15W, 20 W, or any other suitable maximum operating power. The electricalcurrents supplied to pump laser 1 and pump laser 2 may be independentlyadjusted so that the amount of optical power produced by each pump laseris also independently adjustable. The electrical current supplied topump laser 1 or pump laser 2 may be adjustable between any suitablevalues, such as for example, between a minimum current of 0 amperes (or,0 amps) and a maximum current of approximately 1 amp, 2 amps, 5 amps, 10amps, 15 amps, or 20 amps.

In particular embodiments, the wavelength of light produced by a pumplaser diode may vary with temperature by between approximately +0.1nanometers per degree Celsius (nm/° C.) and approximately +0.5 nm/° C.As an example, the operating wavelength of pump laser 1 or pump laser 2may vary with a temperature change of the pump laser by approximately+0.3 nm/° C. If pump laser 1 operates at approximately 920 nm at 25° C.,then the wavelength of pump laser 1 may shift to approximately 923 nm ifthe temperature of pump laser 1 increases by 10° C. to 35° C. If pumplaser 2 operates at approximately 950 nm at 25° C., then the wavelengthof pump laser 2 may shift to approximately 944 nm if the temperature ofpump laser 2 decreases by 20° C. to 5° C. The temperature-dependentwavelength shifts of pump laser 1 and pump laser 2 are illustrated bythe dashed arrows in FIG. 23. If the temperature decreases, then thewavelengths of pump laser 1 and pump laser 2 shift to shorterwavelengths. If the temperature increases, then the wavelengths of pumplaser 1 and pump laser 2 shift to longer wavelengths.

In particular embodiments, a pump laser diode of an optical amplifiermay be passively cooled by being thermally coupled to a heat sink.Passive cooling may refer to dissipation of heat from a pump laser diodeby thermal contact with a heat sink and without the use of an activetemperature-stabilization component (e.g., a TEC). As an example, pumplaser 1 or pump laser 2 in FIG. 20, FIG. 21, or FIG. 22 may be inthermal contact with a heat sink, and pump laser 1 or pump laser 2 maynot include or may not be mounted on a TEC. With passive cooling, theoperating temperature of pump laser 1 or pump laser 2 may not bestabilized to a fixed value, and as the ambient temperature of theamplifier, light source 110, or lidar system 100 changes, the operatingtemperature of pump laser 1 or pump laser 2 may also change. Todissipate heat produced by a pump laser diode, the pump laser diode maybe in thermal contact with a heat sink that receives heat from the pumplaser diode. As an example, pump laser 1 or pump laser 2 in FIG. 20 orFIG. 21 may be packaged in a metal case that is in thermal contact witha heat sink, such as for example, a part of amplifier 470, light source110, or lidar system 100 that conducts or dissipates heat (e.g., athermal mass, a metal block, a metal panel, a heat pipe, a heatspreader, a heat sink, or a fan). As another example, pump laser 1 orpump laser 2 in FIG. 22 may be mechanically attached to and in thermalcontact with platform 905. The platform 905 may be made from a materialwith a relatively high thermal conductivity, and excess heat produced bypump laser 1 or pump laser 2 may flow into the platform 905.Additionally, the platform 905 may be in thermal contact with a heatsink or thermally conductive object that receives or dissipates heatfrom the platform 905.

In particular embodiments, passive cooling of a pump laser diode mayrefer to dissipation of heat from a pump laser diode by thermal contactwith a heat sink where the pump laser diode is not directly coupled toan active temperature-stabilization component. As an example, a pumplaser diode may be mounted to and may be directly thermally coupled to achip carrier which in turn is attached to and thermally coupled to aplatform (e.g., platform 705, platform 805, or platform 905). Theplatform may receive excess heat from the pump laser diode through thechip carrier. The platform may be thermally coupled to a heat sink(e.g., a thermal mass, a metal block, a metal panel, a heat pipe, a heatspreader, or a fan) that receives or dissipates excess heat from theplatform (including heat from the pump laser diode). In particularembodiments, a platform may be thermally coupled to an activetemperature-stabilization component. For example, platform 905 may beattached or coupled to a TEC which operates to maintain the platform 905at a substantially constant temperature. The pump lasers attached to theplatform 905 may be passively cooled by being thermally coupled to theplatform 905, and the TEC may be used to remove excess heat from theplatform 905 or to maintain the platform 905 at a substantially constanttemperature. As another example, platform 905 may be attached or coupledto a TEC which is activated if a temperature reaches, exceeds, or goesbelow a particular threshold temperature (e.g., −20° C., −10° C., 0° C.,30° C., 40° C., 50° C., 60° C., or 70° C.). For example, if thetemperature of platform 905 reaches or exceeds 45° C., then the TEC maybe activated to keep the platform temperature at or below 45° C.Similarly, if the temperature of platform 905 reaches or goes below −10°C., then the TEC or a heating element may be activated to keep theplatform temperature at or above −10° C.

In particular embodiments, the amount of optical power provided by eachpump laser in an optical amplifier with multiple pump lasers may beadjusted based at least in part on an absorption spectrum of the opticalgain fiber. For example, the amount of optical power provided by pumplaser 1 and pump laser 2 in FIG. 20, FIG. 21, or FIG. 22 may be adjustedbased on an absorption spectrum similar to that in FIG. 23. Asillustrated in FIG. 23, an erbium/ytterbium gain fiber has a fairlybroad absorption spectrum that varies with wavelength. Additionally,gain fiber from different manufacturers, different production batches ofgain fiber, or different sections of gain fiber may exhibit variationsin the absorption spectrum. For example, the absorption at 925 nm mayvary between 2 dB/m and 3 dB/m for different erbium/ytterbium gainfibers. In particular embodiments, an absorption spectrum for aparticular section of gain fiber may be characterized to account forabsorption variation with wavelength as well as any batch-to-batchvariations in the absorption spectrum. An optical amplifier thatincludes that particular section of gain fiber may be configured toadjust the optical power provided by each pump laser based at least inpart on the particular absorption spectrum. Additionally, if theabsorption spectrum changes or shifts with temperature, then the amountof optical power provided by each pump laser may be adjusted based onthe temperature dependence of the pump-laser wavelengths or thetemperature dependence of the absorption spectrum of the gain fiber.

In particular embodiments, the amount of optical power produced by pumplaser 1 or pump laser 2 may be adjusted in response to a wavelengthchange of pump laser 1 or pump laser 2, where the wavelength change isassociated with a change in the temperature of pump laser 1 or pumplaser 2. As an example, if pump laser 1 and pump laser 2 are operatingat 920 nm and 950 nm, respectively, a controller may set the current tothe pump lasers so they both produce approximately the same output power(e.g., 5 watts). If the ambient temperature changes, then thewavelengths of pump laser 1 and pump laser 2 may shift (e.g., byapproximately +0.3 nm/° C.), and the amount of absorption of the twopump lasers may change. The controller may adjust the output power ofpump laser 1 or pump laser 2 based on the wavelength shifts and based onthe absorption spectrum of the gain fiber. As an example, if thewavelength of pump laser 1 shifts to a part of the absorption spectrumwith a lower absorption value, then the controller may decrease theamount of power produced by pump laser 1 or may increase the amount ofpower produced by pump laser 2. The power of pump laser 1 may bedecreased since the lower absorption value of the pump-laser lightcorresponds to a reduction in the absorption efficiency of the gainfiber. Additionally, to compensate for the reduced absorption or powerof pump laser 1, the power of pump laser 2 may be increased. As anotherexample, if the wavelength of pump laser 1 shifts to a part of theabsorption spectrum with an increased absorption value, then thecontroller may increase the amount of power produced by pump laser 1 ormay decrease the amount of power produced by pump laser 2. The power ofpump laser 1 may be increased since the increase in absorptionrepresents an increase in the absorption efficiency of the gain fiber,and the power of pump laser 2 may be decreased to compensate for theincreased absorption or power of pump laser 1.

In particular embodiments, pumping a gain fiber with multiple pumplasers operating at multiple wavelengths may be used to mitigate theeffects of pump-laser wavelength drift associated with temperaturechanges. Rather than actively stabilizing the temperature of the pumplasers (e.g., using a TEC) to keep the operating wavelengthssubstantially fixed, the pump lasers may be passively cooled (and theirwavelengths may be allowed to shift with temperature), which maysimplify the design or complexity of an optical amplifier or reduce itscost or power consumption. As the temperature changes and the pump-laserwavelengths shift (e.g., by approximately +0.3 nm/° C.), a controllermay dynamically adjust the power of the pump lasers, based at least inpart on the absorption spectrum of the gain fiber, to optimize thepumping of the gain fiber. Each pump laser may be configured to produceup to approximately 12 watts, and in most operating conditions, the pumplasers may be operated below such a maximum operating power value. Byoperating the pump lasers at reduced output powers (and correspondinglyreduced electrical currents), the pump lasers may operate in a moreefficient manner and may produce less excess waste heat. Additionally,the lifetime of the pump lasers may be extended since they are beingoperated below a maximum operating power or current. By operating thepump lasers at reduced output power and adjusting the output power ofeach of the pump lasers, the performance or efficiency of an opticalamplifier may be improved. Additionally, the pump lasers may be lesssusceptible to problems with thermal runaway in which a pump laser maybe damaged or its performance may degrade if the temperature increases.

In particular embodiments, an optical amplifier may include one or moretemperature sensors configured to measure a temperature of pump laser 1,a temperature of pump laser 2, a temperature of the optical amplifier,or a temperature of lidar system 100. As an example, a temperaturesensor (e.g., a thermistor or a thermocouple) may be located near or maybe thermally coupled to pump laser 1 or pump laser 2. The temperaturesensor may measure a temperature of a block, mount, or chip carrier thatpump laser 1 or pump laser 2 is attached to or thermally coupled to. Asanother example, a temperature sensor may be attached to or located neara part of an optical amplifier or lidar system 100. A temperature sensormay monitor the air temperature or an ambient temperature within anoptical amplifier enclosure or a lidar-system enclosure, or atemperature sensor may be attached to part of an optical amplifier orpart of a lidar system 100. For example, a temperature sensor may beattached to a part of amplifier 470 in FIG. 20 or FIG. 21, or atemperature sensor may be attached to a platform 905 of amplifierassembly 900 in FIG. 22.

In particular embodiments, an optical amplifier may include a singletemperature sensor or may include multiple temperature sensors. Forexample, an optical amplifier may include one temperature sensor, andthe temperature-dependent wavelength variation of pump laser 1 and pumplaser 2 may be determined based on the temperature reading from the onetemperature sensor. As another example, an optical amplifier may includeone temperature sensor that monitors the temperature of pump laser 1 andanother temperature sensor that monitors the temperature of pump laser2. The temperature-dependent wavelength variation of each pump laser maybe determined based on its associated temperature sensor.

In particular embodiments, the amount of optical power produced by pumplaser 1 and pump laser 2 may be adjusted in response to a change in atemperature of pump laser 1, a change in a temperature of pump laser 2,or a change in a temperature of the optical amplifier. As an example, anoptical amplifier (e.g., amplifier 470 in FIG. 20 or FIG. 21 oramplifier assembly 900 in FIG. 22) may include one temperature sensor.The amount of optical power produced by pump laser 1 may be adjusted inresponse to a temperature change determined from the temperature sensor.Similarly, the amount of optical power produced by pump laser 2 may beadjusted in response to a temperature change determined from thetemperature sensor. As another example, an optical amplifier may includea first temperature sensor thermally coupled to pump laser 1 and asecond temperature sensor thermally coupled to pump laser 2. The amountof optical power produced by pump laser 1 may be adjusted in response toa temperature change determined from the first temperature sensor.Similarly, the amount of optical power produced by pump laser 2 may beadjusted in response to a temperature change determined from the secondtemperature sensor. In particular embodiments, a temperature sensor maybe electrically coupled to a pump-laser driver (e.g., pump-laser driver938A or 938B in FIG. 22) or a controller, and the pump-laser driver orcontroller may receive or monitor a signal from the temperature sensor.As an example, a pump-laser driver or controller may determine that atemperature change has occurred (e.g., based on an electrical signalreceived from a temperature sensor), and the pump-laser driver orcontroller may adjust the current supplied to a pump laser in responseto the temperature change.

In particular embodiments, the amounts of optical power produced by pumplaser 1 and pump laser 2 may be adjusted in a reverse or oppositemanner. As an example, if the amount of optical power produced by pumplaser 1 is increased, then the amount of optical power produced by pumplaser 2 may be decreased or may remain unchanged. Similarly, if theamount of optical power produced by pump laser 1 is decreased, then theamount of optical power produced by pump laser 2 may be increased or mayremain unchanged. As another example, if pump laser 1 and pump laser 2are each operating with an output optical power of approximately 5 W,then in response to an increase in the temperature of pump laser 1 orpump laser 2, a controller may increase the output power of pump laser 1(e.g., to 6 W) and may decrease the output power of pump laser 2 (e.g.,to 4 W). Similarly, in response to a decrease in the temperature of pumplaser 1 or pump laser 2, a controller may decrease the output power ofpump laser 1 and may increase the output power of pump laser 1.Increasing or decreasing the output power of a pump laser may includeincreasing or decreasing the electrical current supplied to the pumplaser. For example, a controller may send a signal or instruction to apump-laser driver to increase or decrease the electrical current.

In particular embodiments, adjusting the amount of optical powerproduced by a pump laser may include increasing the amount of opticalpower, decreasing the amount of optical power, or leaving the amount ofoptical power substantially unchanged. As an example, in response to anincrease or decrease in the temperature of pump laser 1 or pump laser 2,a controller may increase or decrease the output power of pump laser 1and may keep the output power of pump laser 2 substantially unchanged.As another example, if pump laser 1 and pump laser 2 are each operatingwith an output optical power of approximately 5 W, then in response to adecrease in the temperature of pump laser 1 or pump laser 2, acontroller may increase the output power of pump laser 1 (e.g., to 7 W)and may leave the output power of pump laser 2 unchanged at 5 W.

FIG. 24 illustrates an example lookup table for adjusting pump-lasercurrent based on temperature. A lookup table may be determined during afactory calibration procedure and may be used to set the current or theoutput power of a pump laser based on a temperature reading. Inparticular embodiments, the amounts of optical power produced by pumplaser 1 and pump laser 2 may be adjusted based on a lookup table. Alookup table may include drive currents for the pump lasers of anoptical amplifier and one or more temperature values. For example, alookup table may include temperature values for pump laser 1 and pumplaser 2 along with corresponding drive current values for pump laser 1and pump laser 2. The lookup table in FIG. 24 provides the electricaldrive currents for pump laser 1 and pump laser 2 at differenttemperatures from 0° C. to 70° C. The temperature may correspond to thetemperature of pump laser 1 or pump laser 2, a temperature of anotherpart of the optical amplifier (e.g., a temperature of platform 905), ora temperature of the lidar system 100. As an example, if the temperatureof pump laser 1 is 50° C., then the drive current for pump laser 1 maybe set to 4 amps. If the temperature of pump laser 1 decreases to 40°C., then the drive current for pump laser 1 may be increased to 5 amps.As another example, if the temperature of platform 905 is 10° C., thenthe drive currents for pump laser 1 and pump laser 2 may be set to 8amps and 3 amps, respectively. If the platform temperature increases to20° C., then the drive currents for pump laser 1 and pump laser 2 may bechanged to 7 amps and 4 amps, respectively.

In particular embodiments, the current settings for pump laser 1 andpump laser 2 may be adjusted in a reverse or opposite manner. As anexample, from the lookup table in FIG. 24, as the temperature changesfrom 0° C. to 70° C., the current settings for pump laser 1 decreasefrom 8 amps to 2 amps, and the current settings for pump laser 2increase from 2 amps to 8 amps. For some temperature changes, the valuesfor pump-laser current in a lookup table may remain unchanged. Forexample, in FIG. 24, if the temperature changes from 0° C. to 10° C.,the current for pump laser 1 remains fixed at 8 amps, while the currentfor pump laser 2 changes from 2 amps to 3 amps. In particularembodiments, a lookup table may include any suitable number oftemperature and current entries with any suitable temperature intervalbetween successive entries. As an example, a lookup table may includesuccessive temperature values in increments of approximately 10° C. (asillustrated in FIG. 24), 5° C., 1° C., 0.5° C., or 0.1° C. In particularembodiments, setpoint values for pump-laser currents may be determinedby interpolating between two adjacent setpoint values in a lookup table.As an example, based on FIG. 24, if the temperature is 25° C., then thecurrents for pump laser 1 and pump laser 2 may be set to approximately6.5 amps and 4.5 amps, respectively.

In particular embodiments, an optical amplifier may include two or morepump laser diodes, where each pump laser diode emits light from a backfacet that is received by a corresponding pump-laser detector (which maybe referred to as a back-facet detector or a back-facet monitor). As anexample, pump laser 1 and pump laser 2 in FIG. 20 or FIG. 21 may eachinclude a pump-laser detector configured to receive back-facet light. InFIG. 22, back-facet light 932A from pump laser 1 is received bypump-laser detector 936A, and back-facet light 932B from pump laser 2 isreceived by pump-laser detector 936B. In particular embodiments, acontroller may adjust the amount of optical power produced by a pumplaser based at least in part on an electrical signal received from apump-laser detector. As an example, in FIG. 22, the optical powerproduced by pump laser 1 and pump laser 2 may be adjusted based onelectrical signals from pump-laser detector 936A and pump-laser detector936B, respectively. The electrical signal from a pump-laser detector maycorrespond to the amount of back-facet light received by the detector,which in turn may correspond to the amount of optical power produced bythe pump laser. For example, the electrical signal from pump-laserdetector 936A may correspond to the optical power of pump-laserback-facet light 932A, which in turn may correspond to the optical powerof pump-laser beam 934A.

In particular embodiments, a controller may adjust the amount ofelectrical current supplied to a pump laser based at least in part on anelectrical signal received from a pump-laser detector. As an example,rather than supplying a substantially constant current to a pump laser,a controller may be configured to maintain a substantially constantoutput power from the pump laser by adjusting the pump-laser current inresponse to changes in the pump-laser detector signal. As a pump laserages or as its performance degrades, it may produce less optical powerfor a particular current, and the controller may increase the current tothe pump laser to maintain a substantially constant signal from thepump-laser detector (which may correspond to a substantially constantpump-laser output power). For example, a relatively new pump laser mayproduce 8 W of output power with a pump-laser current of 9 amps, andafter 1,000 hours of operation, 10 amps of current may be required toproduce the same 8-W output power. In particular embodiments, acontroller may adjust the current to a pump laser based on a lookuptable that relates a temperature with a pump-laser detector signal. Ifthe temperature changes, rather than adjusting the current to aparticular value based on the temperature, the controller may insteadadjust the pump-laser current until a particular pump-laser detectorsignal is reached (which corresponds to a particular pump-laser outputpower).

In particular embodiments, the amount of optical power produced by oneor more pump lasers may be adjusted in response to a change in an amountof residual pump light detected at or near an output end of an opticalgain fiber. Rather than setting the pump-laser power or current based ona temperature measurement, the pump-laser power or current may be setbased at least in part on a measurement of the power of residual pumplight. Residual pump light may refer to pump light that reaches theoutput of a gain fiber without being absorbed while propagating throughthe gain fiber. The residual pump light may correspond to approximately10%, 5%, 2%, 1%, 0.5%, 0.1%, or any other suitable percentage of thepump power at the input of a gain fiber. As an example, if the pumppower at the input of a gain fiber is 10 W, approximately 9.8 W of thepump light may be absorbed by the gain fiber, and there may beapproximately 200 mW of residual pump light, which corresponds to 2% ofthe input pump power.

In particular embodiments, the amount of residual pump light at theoutput end of a gain fiber may be determined using one or more detectorsconfigured to receive at least part of the residual pump light. Theresidual pump light may include a combination of residual light frompump laser 1 and pump laser 2. The output end of a gain fiber (e.g.,gain fiber 660 in FIG. 20 or FIG. 21, or gain fiber 960 in FIG. 22) mayinclude one or more detectors configured to detect at least a portion ofthe residual pump light from pump laser 1 or pump laser 2. As anexample, a coupler or filter located at the output end of a gain fibermay direct at least part of the residual pump light to one or moredetectors (e.g., one filter may transmit light from pump laser 1 andblock or reflect light from pump laser 2). As another example, acladding power stripper located at the output end of a gain fiber mayremove residual pump light from the gain fiber, and at least part of theresidual light may be received by one or more detectors (e.g., adetector may include a filter that transmits light from pump laser 1 andblocks or reflects light from pump laser 2). As another example, one ormore detectors may be coupled to one of the pump ports of a (N+1)×1fiber-optic combiner, and the detectors may be used to detect residualpump light. For example, an optical amplifier may include two pumplasers located at opposite ends of a gain fiber (e.g., a co-propagatingpump laser and a counter-propagating pump laser). The light from eachpump laser may be combined with input light to be amplified using a(2+1)×1 fiber-optic combiner, and a detector may be coupled to the otherpump port of the combiner. The detector may be used to detect residualpump light from the pump laser located at the opposite end of the gainfiber.

In particular embodiments, the output end of a gain fiber may includeone detector (e.g., a silicon, germanium, or InGaAs PN or PINphotodiode) that receives at least part of the residual light andproduces an electrical signal that corresponds to the amount of receivedresidual light. For example, a silicon photodiode may be used to detectresidual pump light, and the silicon photodiode (which may detect lightbetween approximately 400 nm and approximately 1100 nm) may not besensitive to the amplified light which may have a wavelength in the1400-1600 nm range. In particular embodiments, the output end of a gainfiber may include two or more detectors configured to receive at leastpart of the residual light. As an example, an optical amplifier mayinclude two pump lasers (e.g., pump laser 1 and pump laser 2), and twodetectors may be located at or near the output end of the gain fiber.One detector may be configured to receive at least part of the residuallight from pump laser 1, and the other detector may be configured toreceive at least part of the residual light from pump laser 2. As anexample, pump laser 1 and pump laser 2 may operate at differentwavelengths, and each detector may include a filter that transmits lightfrom one pump laser and blocks light from the other pump laser. Forexample, pump laser 1 may operate at a wavelength that varies fromapproximately 915 nm to approximately 935 nm as the temperature variesbetween 0° C. and 70° C., and pump laser 2 may operate fromapproximately 940 nm to approximately 960 nm. The output end of the gainfiber may include a first detector with a filter that transmits 915-935nm light and blocks 940-960 nm light so that the detector receives lightfrom pump laser 1. The output end of the gain fiber may include a seconddetector with a filter that blocks 915-935 nm light and transmits940-960 nm light so that the detector receives light from pump laser 2.Using two detectors with filters may allow the residual light from pumplaser 1 and the residual light from pump laser 2 to be detected ormonitored separately. Additionally, using two detectors with filters mayallow the absorption in the gain fiber of light from pump laser 1 andpump laser 2 to be monitored separately.

In particular embodiments, adjusting the amount of pump-laser power foran optical amplifier with two or more pump lasers may include increasingor decreasing the power of a pump laser based on a change in the amountof residual pump light for one or more of the pump lasers. As anexample, for an optical amplifier with two pump lasers (e.g., pump laser1 and pump laser 2), if the amount of residual pump light associatedwith pump laser 1 increases, then the power of pump laser 1 may bedecreased. An increase in residual pump light may indicate that thewavelength of pump laser 1 has shifted to a wavelength with a lowerabsorption in the gain fiber, and the power of pump laser 1 may bereduced since a lower absorption corresponds to a reduced absorptionefficiency of the gain fiber. Additionally or alternatively, if theamount of residual pump light associated with pump laser 1 increases,then the power of pump laser 2 may be increased to compensate for thereduced absorption of pump laser 1. As another example, if the amount ofresidual pump light associated with pump laser 1 decreases, then thepower of pump laser 1 may be increased. A decrease in residual pumplight may indicate that pump laser 1 has shifted to a higher-absorptionwavelength, and the power of pump laser 1 may be increased to takeadvantage of the increased absorption efficiency of the gain fiber.Additionally or alternatively, if the amount of residual pump lightassociated with pump laser 1 decreases, then the power of pump laser 2may be decreased to compensate for the increased absorption of pumplaser 1.

In particular embodiments, the amount of optical power produced by oneor more pump lasers may be adjusted in response to a change in an amountof power of an optical signal after propagating through an optical gainfiber. As an example, an optical signal that propagates through a gainfiber may include optical pulses at 1500-1600 nm which are amplifiedwhile propagating through the gain fiber. A portion of the amplifiedoptical signal at the output end of the gain fiber may be received by adetector (e.g., similar to PD 610B in FIG. 20). If the power of theamplified optical signal decreases, then the power of pump laser 1 orpump laser 2 may be increased to increase the optical gain in the gainfiber (which may result in a corresponding increase in the power of theamplified optical signal). If the power of the amplified optical signalincreases, then the power of pump laser 1 or pump laser 2 may bedecreased to decrease the optical gain in the gain fiber.

In particular embodiments, an optical amplifier may include two or morepump laser diodes, and a controller may be configured to determinewhether a pump laser diode has failed or is beginning to fail. As anexample, an optical amplifier, a light source 110, or a lidar system 100may include a controller configured to monitor or determine the healthstatus of the pump lasers of the optical amplifier. If a pump laser isbeginning to fail or has failed, then the optical power produced by thepump laser (at a particular pump-laser current) may decrease, or thecurrent necessary to produce a particular output power may increase. Asan example, a pump laser that is operating normally (e.g., the pumplaser is not failing) may produce approximately 8 W of output power fora 10-amp pump-laser current. If the output power of the pump laser dropsbelow a threshold value (e.g., if the output power drops below 7 W for a10-amp pump current), then this may be an indication that the pump laseris beginning to fail. For a particular pump current, a decrease in theoutput power of a pump laser by a particular amount (e.g., a decreasewith respect to a normal output power of greater than 5%, 10%, 20%, 40%,or any other suitable percentage) may indicate that the pump laser isbeginning to fail. A decrease in the output power of a pump laser diodefrom 8 W to 7 W (for a particular pump-laser current) corresponds to a12.5% decrease in output power. As another example, if the pump-lasercurrent necessary to produce 8 W of output power increases above somethreshold value (e.g., above 12 amps), then the pump laser may bebeginning to fail. An increase in the pump-laser current necessary toproduce a particular output power (e.g., an increase with respect to anormal current value of greater than 5%, 10%, 20%, 40%, or any othersuitable percentage) may indicate that the pump laser is beginning tofail. An increase in the current necessary to produce 8 W of outputpower from 10 amps to 12 amps corresponds to a 20% increase in thepump-laser current.

In particular embodiments, the health status of a pump laser may bedetermined based on an electrical signal from a detector (e.g., apump-laser detector) that receives a portion of light emitted by thepump laser. As an example, an optical amplifier may include two pumplaser diodes (e.g., pump laser 1 and pump laser 2), and a controller ora pump-laser driver may receive electrical signals from twocorresponding pump-laser detectors (e.g., pump-laser detectors 936A and936B). A pump-laser detector may generate an electrical signal based onthe amount of back-facet light received from a pump laser. If a pumplaser is beginning to fail, the amount of received back-facet light maydecrease, and the corresponding electrical signal from the pump-laserdetector may change accordingly. A controller or pump-laser driver maymonitor the electrical signal from a pump-laser detector to determinewhether the associated pump laser is beginning to fail. In FIG. 22, fora particular pump-laser current applied to pump laser 1, if theelectrical signal from pump-laser detector 936A drops below a thresholdvalue (or drops by a particular percentage), then this may indicate thatpump laser 1 is beginning to fail. Alternatively, if the pump-lasercurrent necessary to maintain the electrical signal from the pump-laserdetector 936A at a particular level increases above a threshold value(or increases by a particular percentage), then this may indicate thatpump laser 1 is beginning to fail.

In particular embodiments, if one pump laser diode in an opticalamplifier has failed or is beginning to fail, then the amount of opticalpower produced by another pump laser diode may be increased tocompensate for the failing pump laser diode. Having two or moreredundant pump laser diodes may improve the reliability of an opticalamplifier since the optical amplifier may still be able to operate ifone pump laser fails or begins to fail. The two pump lasers in FIG. 20,FIG. 21, or FIG. 22 may act as redundant pump lasers in case one of theother pump lasers fail. Two pump lasers which operate as redundantsources of pump light may operate at different wavelengths or mayoperate at substantially the same wavelength. In FIG. 22, if pump laser1 is beginning to fail, then a controller may send an instruction topump-laser driver 938B to increase the output power of pump laser 2. Asan example, pump laser 1 and pump laser 2 may each be configured toproduce 5 W of pump power. If pump laser 1 begins to fail and its outputpower drops to 2 W, then the current supplied to pump laser 2 may beincreased so that pump laser 2 produces approximately 8 W. Additionally,if pump laser 1 fails and does not produce any significant output power,then the power of pump laser 2 may be increased to approximately 10 W.

In particular embodiments, if one pump laser diode is failing, then thecurrent or the output power of another pump laser diode may be increasedabove a recommended maximum operating current or power. A maximumoperating current or power may be based on information in amanufacturer's data sheet or user's manual. As an example, a pump lasermay have a maximum recommended operating current of 10 amps or a maximumrecommended operating power of 12 watts. The pump laser may be capableof operating above those maximum recommended values, but the lifetime ofthe pump laser may be shortened. For example, a pump laser operatingwith a current of 10 amps may have an estimated lifetime of greater than10,000 hours, and overdriving the pump laser with a current of 12 ampsmay reduce the estimated lifetime to less than 1,000 hours. In FIG. 22,if pump laser 1 is failing or has failed, then pump laser 2 may beoperated at a current or power that is above a maximum operating currentor power. Running pump laser 2 above a maximum operating value may allowthe optical amplifier to continue to operate, at the expense of apossible reduction in the lifetime of pump laser 2.

In particular embodiments, a controller may be configured to send anotification that a pump laser diode has failed or is beginning to fail.As an example, in FIG. 22, if pump laser 1 is failing, a controller maysend a notification indicating that the lidar system 100 should be takenin for service (e.g., to repair or replace the pump laser, the opticalamplifier, or the lidar system). The controller may send a notificationto a server, a controller of a vehicle in which the lidar system isinstalled, or an operator of the vehicle in which the lidar system isinstalled. For example, the controller may send a notificationindicating that the lidar system or the vehicle should be taken in forservice. Additionally, the controller may send an instruction toincrease the current or output power of pump laser 2 to compensate forthe reduced power of pump laser 1 and to allow the optical amplifier tocontinue to operate until the optical amplifier can be repaired orreplaced.

FIG. 25 illustrates an example method 1000 for adjusting the opticalpower provided by pump lasers in an optical amplifier. The method maybegin at step 1010, where pump light having a first amount of opticalpower at a first wavelength is produced by a first pump laser diode. Atstep 1020, pump light having a second amount of optical power at asecond wavelength is produced by a second pump laser diode. Inparticular embodiments, the first wavelength may be different from thesecond wavelength, or the first and second wavelengths may besubstantially the same. As an example, pump laser 1 may produceapproximately 5 W of optical power at approximately 920 nm, and pumplaser 2 may produce approximately 5 W of optical power at approximately950 nm. As another example, pump laser 1 and pump laser 2 may producelight at approximately the same wavelength (e.g., 940 nm±4 nm). At step1030, an optical gain fiber (e.g., gain fiber 660, gain fiber 760, gainfiber 860, or gain fiber 960) may receive the pump light from the firstand second pump laser diodes. At step 1040, the gain fiber may provideoptical gain for an optical signal propagating through the gain fiber.As an example, 900-1000 nm light from two or more pump lasers may beabsorbed by gain material in the gain fiber, and an optical signal thatincludes 1500-1600 nm optical pulses may be amplified while propagatingthrough the gain fiber. At step 1050, a controller (e.g., controller 150in lidar system 100, or another processor located in the opticalamplifier or the lidar system 100) may adjust the first amount ofoptical power produced by the first pump laser diode and the secondamount of optical power produced by the second pump laser diode, atwhich point the method 1000 may end. In particular embodiments, thefirst and second amounts of optical power may be adjusted in response tomeasuring a change in an ambient temperature (e.g., a temperature of theoptical amplifier or of the lidar system 100), a temperature of thefirst pump laser diode, or a temperature of the second pump laser diode.As an example, if the temperature increases, then the first amount ofoptical power may be increased or may remain unchanged, or the secondamount of optical power may be decreased or may remain unchanged. If thetemperature decreases, then the first amount of optical power may bedecreased or may remain unchanged, or the second amount of optical powermay be increased or may remain unchanged. In particular embodiments, thefirst and second amounts of optical power may be adjusted in response todetermining that the first pump laser diode is beginning to fail. As anexample, if pump laser 1 is beginning to fail, the amount of opticalpower produced pump laser 2 may be increased to compensate for thefailing pump laser 1. In particular embodiments, increasing the amountof optical power produced by pump laser 2 may include operating pumplaser 2 above a recommended maximum operating current or power.

FIG. 26 illustrates an example computer system 1100. In particularembodiments, one or more computer systems 1100 may perform one or moresteps of one or more methods described or illustrated herein. Inparticular embodiments, one or more computer systems 1100 may providefunctionality described or illustrated herein. In particularembodiments, software running on one or more computer systems 1100 mayperform one or more steps of one or more methods described orillustrated herein or may provide functionality described or illustratedherein. Particular embodiments may include one or more portions of oneor more computer systems 1100. In particular embodiments, a computersystem may be referred to as a processor, a controller, a computingdevice, a computing system, a computer, a general-purpose computer, or adata-processing apparatus. Herein, reference to a computer system mayencompass one or more computer systems, where appropriate.

Computer system 1100 may take any suitable physical form. As an example,computer system 1100 may be an embedded computer system, asystem-on-chip (SOC), a single-board computer system (SBC), a desktopcomputer system, a laptop or notebook computer system, a mainframe, amesh of computer systems, a server, a tablet computer system, or anysuitable combination of two or more of these. As another example, all orpart of computer system 1100 may be combined with, coupled to, orintegrated into a variety of devices, including, but not limited to, acamera, camcorder, personal digital assistant (PDA), mobile telephone,smartphone, electronic reading device (e.g., an e-reader), game console,smart watch, clock, calculator, television monitor, flat-panel display,computer monitor, vehicle display (e.g., odometer display or dashboarddisplay), vehicle navigation system, lidar system, ADAS, autonomousvehicle, autonomous-vehicle driving system, cockpit control, camera viewdisplay (e.g., display of a rear-view camera in a vehicle), eyewear, orhead-mounted display. Where appropriate, computer system 1100 mayinclude one or more computer systems 1100; be unitary or distributed;span multiple locations; span multiple machines; span multiple datacenters; or reside in a cloud, which may include one or more cloudcomponents in one or more networks. Where appropriate, one or morecomputer systems 1100 may perform without substantial spatial ortemporal limitation one or more steps of one or more methods describedor illustrated herein. As an example, one or more computer systems 1100may perform in real time or in batch mode one or more steps of one ormore methods described or illustrated herein. One or more computersystems 1100 may perform at different times or at different locationsone or more steps of one or more methods described or illustratedherein, where appropriate.

As illustrated in the example of FIG. 26, computer system 1100 mayinclude a processor 1110, memory 1120, storage 1130, an input/output(I/O) interface 1140, a communication interface 1150, or a bus 1160.Computer system 1100 may include any suitable number of any suitablecomponents in any suitable arrangement.

In particular embodiments, processor 1110 may include hardware forexecuting instructions, such as those making up a computer program. Asan example, to execute instructions, processor 1110 may retrieve (orfetch) the instructions from an internal register, an internal cache,memory 1120, or storage 1130; decode and execute them; and then writeone or more results to an internal register, an internal cache, memory1120, or storage 1130. In particular embodiments, processor 1110 mayinclude one or more internal caches for data, instructions, oraddresses. Processor 1110 may include any suitable number of anysuitable internal caches, where appropriate. As an example, processor1110 may include one or more instruction caches, one or more datacaches, or one or more translation lookaside buffers (TLBs).Instructions in the instruction caches may be copies of instructions inmemory 1120 or storage 1130, and the instruction caches may speed upretrieval of those instructions by processor 1110. Data in the datacaches may be copies of data in memory 1120 or storage 1130 forinstructions executing at processor 1110 to operate on; the results ofprevious instructions executed at processor 1110 for access bysubsequent instructions executing at processor 1110 or for writing tomemory 1120 or storage 1130; or other suitable data. The data caches mayspeed up read or write operations by processor 1110. The TLBs may speedup virtual-address translation for processor 1110. In particularembodiments, processor 1110 may include one or more internal registersfor data, instructions, or addresses. Processor 1110 may include anysuitable number of any suitable internal registers, where appropriate.Where appropriate, processor 1110 may include one or more arithmeticlogic units (ALUs); may be a multi-core processor; or may include one ormore processors 1110.

In particular embodiments, memory 1120 may include main memory forstoring instructions for processor 1110 to execute or data for processor1110 to operate on. As an example, computer system 1100 may loadinstructions from storage 1130 or another source (such as, for example,another computer system 1100) to memory 1120. Processor 1110 may thenload the instructions from memory 1120 to an internal register orinternal cache. To execute the instructions, processor 1110 may retrievethe instructions from the internal register or internal cache and decodethem. During or after execution of the instructions, processor 1110 maywrite one or more results (which may be intermediate or final results)to the internal register or internal cache. Processor 1110 may thenwrite one or more of those results to memory 1120. One or more memorybuses (which may each include an address bus and a data bus) may coupleprocessor 1110 to memory 1120. Bus 1160 may include one or more memorybuses. In particular embodiments, one or more memory management units(MMUs) may reside between processor 1110 and memory 1120 and facilitateaccesses to memory 1120 requested by processor 1110. In particularembodiments, memory 1120 may include random access memory (RAM). ThisRAM may be volatile memory, where appropriate. Where appropriate, thisRAM may be dynamic RAM (DRAM) or static RAM (SRAM). Memory 1120 mayinclude one or more memories 1120, where appropriate.

In particular embodiments, storage 1130 may include mass storage fordata or instructions. As an example, storage 1130 may include a harddisk drive (HDD), a floppy disk drive, flash memory, an optical disc, amagneto-optical disc, magnetic tape, or a Universal Serial Bus (USB)drive or a combination of two or more of these. Storage 1130 may includeremovable or non-removable (or fixed) media, where appropriate. Storage1130 may be internal or external to computer system 1100, whereappropriate. In particular embodiments, storage 1130 may benon-volatile, solid-state memory. In particular embodiments, storage1130 may include read-only memory (ROM). Where appropriate, this ROM maybe mask ROM (MROM), programmable ROM (PROM), erasable PROM (EPROM),electrically erasable PROM (EEPROM), flash memory, or a combination oftwo or more of these. Storage 1130 may include one or more storagecontrol units facilitating communication between processor 1110 andstorage 1130, where appropriate. Where appropriate, storage 1130 mayinclude one or more storages 1130.

In particular embodiments, I/O interface 1140 may include hardware,software, or both, providing one or more interfaces for communicationbetween computer system 1100 and one or more I/O devices. Computersystem 1100 may include one or more of these I/O devices, whereappropriate. One or more of these I/O devices may enable communicationbetween a person and computer system 1100. As an example, an I/O devicemay include a keyboard, keypad, microphone, monitor, mouse, printer,scanner, speaker, camera, stylus, tablet, touch screen, trackball,another suitable I/O device, or any suitable combination of two or moreof these. An I/O device may include one or more sensors. Whereappropriate, I/O interface 1140 may include one or more device orsoftware drivers enabling processor 1110 to drive one or more of theseI/O devices. I/O interface 1140 may include one or more I/O interfaces1140, where appropriate.

In particular embodiments, communication interface 1150 may includehardware, software, or both providing one or more interfaces forcommunication (such as, for example, packet-based communication) betweencomputer system 1100 and one or more other computer systems 1100 or oneor more networks. As an example, communication interface 1150 mayinclude a network interface controller (NIC) or network adapter forcommunicating with an Ethernet or other wire-based network or a wirelessNIC (WNIC); a wireless adapter for communicating with a wirelessnetwork, such as a WI-FI network; or an optical transmitter (e.g., alaser or a light-emitting diode) or an optical receiver (e.g., aphotodetector) for communicating using fiber-optic communication orfree-space optical communication. Computer system 1100 may communicatewith an ad hoc network, a personal area network (PAN), an in-vehiclenetwork (IVN), a local area network (LAN), a wide area network (WAN), ametropolitan area network (MAN), or one or more portions of the Internetor a combination of two or more of these. One or more portions of one ormore of these networks may be wired or wireless. As an example, computersystem 1100 may communicate with a wireless PAN (WPAN) (such as, forexample, a BLUETOOTH WPAN), a WI-FI network, a WorldwideInteroperability for Microwave Access (WiMAX) network, a cellulartelephone network (such as, for example, a Global System for MobileCommunications (GSM) network), or other suitable wireless network or acombination of two or more of these. As another example, computer system1100 may communicate using fiber-optic communication based on 100Gigabit Ethernet (100 GbE), 10 Gigabit Ethernet (10 GbE), or SynchronousOptical Networking (SONET). Computer system 1100 may include anysuitable communication interface 1150 for any of these networks, whereappropriate. Communication interface 1150 may include one or morecommunication interfaces 1150, where appropriate.

In particular embodiments, bus 1160 may include hardware, software, orboth coupling components of computer system 1100 to each other. As anexample, bus 1160 may include an Accelerated Graphics Port (AGP) orother graphics bus, a controller area network (CAN) bus, an EnhancedIndustry Standard Architecture (EISA) bus, a front-side bus (FSB), aHYPERTRANSPORT (HT) interconnect, an Industry Standard Architecture(ISA) bus, an INFINIBAND interconnect, a low-pin-count (LPC) bus, amemory bus, a Micro Channel Architecture (MCA) bus, a PeripheralComponent Interconnect (PCI) bus, a PCI-Express (PCIe) bus, a serialadvanced technology attachment (SATA) bus, a Video Electronics StandardsAssociation local bus (VLB), or another suitable bus or a combination oftwo or more of these. Bus 1160 may include one or more buses 1160, whereappropriate.

In particular embodiments, various modules, circuits, systems, methods,or algorithm steps described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or any suitable combination of hardware and software. Inparticular embodiments, computer software (which may be referred to assoftware, computer-executable code, computer code, a computer program,computer instructions, or instructions) may be used to perform variousfunctions described or illustrated herein, and computer software may beconfigured to be executed by or to control the operation of computersystem 1100. As an example, computer software may include instructionsconfigured to be executed by processor 1110. In particular embodiments,owing to the interchangeability of hardware and software, the variousillustrative logical blocks, modules, circuits, or algorithm steps havebeen described generally in terms of functionality. Whether suchfunctionality is implemented in hardware, software, or a combination ofhardware and software may depend upon the particular application ordesign constraints imposed on the overall system.

In particular embodiments, a computing device may be used to implementvarious modules, circuits, systems, methods, or algorithm stepsdisclosed herein. As an example, all or part of a module, circuit,system, method, or algorithm disclosed herein may be implemented orperformed by a general-purpose single- or multi-chip processor, adigital signal processor (DSP), an ASIC, a FPGA, any other suitableprogrammable-logic device, discrete gate or transistor logic, discretehardware components, or any suitable combination thereof. Ageneral-purpose processor may be a microprocessor, or, any conventionalprocessor, controller, microcontroller, or state machine. A processormay also be implemented as a combination of computing devices, e.g., acombination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

In particular embodiments, one or more implementations of the subjectmatter described herein may be implemented as one or more computerprograms (e.g., one or more modules of computer-program instructionsencoded or stored on a computer-readable non-transitory storage medium).As an example, the steps of a method or algorithm disclosed herein maybe implemented in a processor-executable software module which mayreside on a computer-readable non-transitory storage medium. Inparticular embodiments, a computer-readable non-transitory storagemedium may include any suitable storage medium that may be used to storeor transfer computer software and that may be accessed by a computersystem. Herein, a computer-readable non-transitory storage medium ormedia may include one or more semiconductor-based or other integratedcircuits (ICs) (such, as for example, field-programmable gate arrays(FPGAs) or application-specific ICs (ASICs)), hard disk drives (HDDs),hybrid hard drives (HHDs), optical discs (e.g., compact discs (CDs),CD-ROM, digital versatile discs (DVDs), blue-ray discs, or laser discs),optical disc drives (ODDs), magneto-optical discs, magneto-opticaldrives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes,flash memories, solid-state drives (SSDs), RAM, RAM-drives, ROM, SECUREDIGITAL cards or drives, any other suitable computer-readablenon-transitory storage media, or any suitable combination of two or moreof these, where appropriate. A computer-readable non-transitory storagemedium may be volatile, non-volatile, or a combination of volatile andnon-volatile, where appropriate.

In particular embodiments, certain features described herein in thecontext of separate implementations may also be combined and implementedin a single implementation. Conversely, various features that aredescribed in the context of a single implementation may also beimplemented in multiple implementations separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination may in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

While operations may be depicted in the drawings as occurring in aparticular order, this should not be understood as requiring that suchoperations be performed in the particular order shown or in sequentialorder, or that all operations be performed. Further, the drawings mayschematically depict one more example processes or methods in the formof a flow diagram or a sequence diagram. However, other operations thatare not depicted may be incorporated in the example processes or methodsthat are schematically illustrated. For example, one or more additionaloperations may be performed before, after, simultaneously with, orbetween any of the illustrated operations. Moreover, one or moreoperations depicted in a diagram may be repeated, where appropriate.Additionally, operations depicted in a diagram may be performed in anysuitable order. Furthermore, although particular components, devices, orsystems are described herein as carrying out particular operations, anysuitable combination of any suitable components, devices, or systems maybe used to carry out any suitable operation or combination ofoperations. In certain circumstances, multitasking or parallelprocessing operations may be performed. Moreover, the separation ofvarious system components in the implementations described herein shouldnot be understood as requiring such separation in all implementations,and it should be understood that the described program components andsystems may be integrated together in a single software product orpackaged into multiple software products.

Various embodiments have been described in connection with theaccompanying drawings. However, it should be understood that the figuresmay not necessarily be drawn to scale. As an example, distances orangles depicted in the figures are illustrative and may not necessarilybear an exact relationship to actual dimensions or layout of the devicesillustrated.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes or illustrates respective embodimentsherein as including particular components, elements, functions,operations, or steps, any of these embodiments may include anycombination or permutation of any of the components, elements,functions, operations, or steps described or illustrated anywhere hereinthat a person having ordinary skill in the art would comprehend.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination, unless expressly indicated otherwiseor indicated otherwise by context. Therefore, herein, the expression “Aor B” means “A, B, or both A and B.” As another example, herein, “A, Bor C” means at least one of the following: A; B; C; A and B; A and C; Band C; A, B and C. An exception to this definition will occur if acombination of elements, devices, steps, or operations is in some wayinherently mutually exclusive.

As used herein, words of approximation such as, without limitation,“approximately, “substantially,” or “about” refer to a condition thatwhen so modified is understood to not necessarily be absolute or perfectbut would be considered close enough to those of ordinary skill in theart to warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skill in the art recognize themodified feature as having the required characteristics or capabilitiesof the unmodified feature. In general, but subject to the precedingdiscussion, a numerical value herein that is modified by a word ofapproximation such as “approximately” may vary from the stated value by±0.5%, ±1%, ±2%, ±3%, ±4%, ±5%, ±10%, ±12%, or ±15%.

As used herein, the terms “first,” “second,” “third,” etc. may be usedas labels for nouns that they precede, and these terms may notnecessarily imply a particular ordering (e.g., a particular spatial,temporal, or logical ordering). As an example, a system may be describedas determining a “first result” and a “second result,” and the terms“first” and “second” may not necessarily imply that the first result isdetermined before the second result.

As used herein, the terms “based on” and “based at least in part on” maybe used to describe or present one or more factors that affect adetermination, and these terms may not exclude additional factors thatmay affect a determination. A determination may be based solely on thosefactors which are presented or may be based at least in part on thosefactors. The phrase “determine A based on B” indicates that B is afactor that affects the determination of A. In some instances, otherfactors may also contribute to the determination of A. In otherinstances, A may be determined based solely on B.

What is claimed is:
 1. A laser system comprising: a seed laser diodeconfigured to produce a free-space seed-laser beam; a seed-laser lensconfigured to collimate the seed-laser beam; a pump laser diodeconfigured to produce a free-space pump-laser beam; a pump-laser lensconfigured to collimate the pump-laser beam; an optical-beam combinerconfigured to combine the collimated seed-laser and pump-laser beamsinto a combined free-space beam; a focusing lens configured to focus thecombined beam; an optical gain fiber comprising an input end configuredto receive the focused beam; and a mounting platform, wherein one ormore of the seed laser diode, the seed-laser lens, the pump laser diode,the pump-laser lens, the optical-beam combiner, the focusing lens, andthe input end of the optical gain fiber are mechanically attached to themounting platform.
 2. The laser system of claim 1, wherein the mountingplatform comprises a glass, ceramic, semiconductor, or metal materialhaving a relatively low coefficient of thermal expansion or a relativelyhigh thermal conductivity.
 3. The laser system of claim 1, wherein themounting platform comprises one or more mechanical registration featuresconfigured to define a fixed position on the mounting platform for eachof one or more of the seed laser diode, the seed-laser lens, the pumplaser diode, the pump-laser lens, the optical-beam combiner, thefocusing lens, and the input end of the optical gain fiber.
 4. The lasersystem of claim 3, wherein: the mounting platform comprises silicon or asilicon-based material; and the mechanical registration features areproduced through a microfabrication process applied to the mountingplatform.
 5. The laser system of claim 3, wherein one or more of theseed laser diode, the seed-laser lens, the pump laser diode, thepump-laser lens, the optical-beam combiner, the focusing lens, and theinput end of the optical gain fiber are mechanically attached to themounting platform using a passive-alignment technique based on themechanical registration features.
 6. The laser system of claim 1,wherein one or more of the seed laser diode, the seed-laser lens, thepump laser diode, the pump-laser lens, the optical-beam combiner, thefocusing lens, and the input end of the optical gain fiber aremechanically attached to the mounting platform using an active-alignmenttechnique.
 7. The laser system of claim 1, wherein each of the seedlaser diode, the seed-laser lens, the pump laser diode, the pump-laserlens, the optical-beam combiner, the focusing lens, and the input end ofthe optical gain fiber are mechanically attached to the mountingplatform using either a passive-alignment technique or anactive-alignment technique.
 8. The laser system of claim 1, wherein oneor more of the seed laser diode, the seed-laser lens, the pump laserdiode, the pump-laser lens, the optical-beam combiner, the focusinglens, and the input end of the optical gain fiber are mechanicallyattached to the mounting platform by epoxy, solder, or one or moremechanical fasteners.
 9. The laser system of claim 1, wherein themounting platform is contained within an enclosure comprising afeedthrough for the optical gain fiber, wherein the enclosure isconfigured to be purged with an inert gas and sealed.
 10. The lasersystem of claim 1, further comprising an optical isolator configured totransmit the collimated seed-laser beam and prevent light frompropagating back toward the seed laser diode.
 11. The laser system ofclaim 1, further comprising: a seed-laser detector configured to receivelight emitted from a back facet of the seed laser diode; and apump-laser detector configured to receive light emitted from a backfacet of the pump laser diode.
 12. The laser system of claim 1, whereinthe pump-laser lens comprises: a fast-axis collimating lens; and aslow-axis collimating lens.
 13. The laser system of claim 1, wherein:the seed laser diode is configured to produce light at a wavelengthbetween approximately 1500 nm and approximately 1600 nm; and the pumplaser diode is configured to produce light at a wavelength betweenapproximately 900 nm and approximately 1000 nm.
 14. The laser system ofclaim 1, wherein the seed laser diode is configured to be operated in apulsed mode wherein the seed-laser beam comprises optical pulses havinga pulse duration less than or equal to 10 nanoseconds and a duty cycleless than or equal to 1%.
 15. The laser system of claim 1, wherein theoptical gain fiber is configured to: absorb, by a gain material of theoptical gain fiber, at least part of the pump-laser portion of thereceived beam; and amplify, by the gain material, the seed-laser portionof the received beam.
 16. The laser system of claim 1, wherein the inputend of the optical gain fiber comprises an input face with ananti-reflection coating having a low optical reflectivity at awavelength of the seed laser or a wavelength of the pump laser.
 17. Thelaser system of claim 1, wherein the optical gain fiber comprises afiber Bragg grating configured to reflect a portion of light from thepump-laser beam back to the pump laser diode.
 18. The laser system ofclaim 1, wherein the laser system is part of a lidar system comprising ascanner and a receiver, wherein: the laser system provides pulses oflight to the scanner; the scanner scans at least a portion of the pulsesof light across a field of regard of the lidar system; and the receiverdetects at least a portion of the scanned pulses of light scattered by atarget located a distance from the lidar system.
 19. The laser system ofclaim 1, further comprising a booster amplifier comprising: an outputend of the optical gain fiber, wherein the output end is configured toproduce a free-space amplified beam comprising light from the seed laserdiode that is amplified while propagating through the optical gainfiber; a collimating lens configured to collimate the amplified beam; abooster-amplifier pump laser diode configured to produce a free-spacebooster-amplifier pump-laser beam; a booster-amplifier lens configuredto collimate the booster-amplifier pump-laser beam; a booster-amplifierbeam combiner configured to combine the collimated amplified beam andthe collimated booster-amplifier pump-laser beam into a combinedbooster-amplifier beam; a booster-amplifier focusing lens configured tofocus the combined booster-amplifier beam; a multi-clad gain fibercomprising an input end configured to receive the combinedbooster-amplifier beam; and a booster-amplifier mounting platform,wherein one or more of the output end of the optical gain fiber, thecollimating lens, the booster-amplifier pump laser diode, thebooster-amplifier lens, the booster-amplifier beam combiner, thebooster-amplifier focusing lens, and the input end of the multi-cladgain fiber are mechanically attached to the mounting platform.
 20. Thelaser system of claim 19, wherein the multi-clad gain fiber is adual-clad gain fiber comprising a core, an inner cladding, and an outercladding, wherein the core, inner cladding, and outer cladding eachcomprises a glass material.
 21. The laser system of claim 19, whereinthe multi-clad gain fiber is a triple-clad gain fiber comprising a core,and three cladding layers, wherein the core and cladding layers eachcomprises a glass material.
 22. The laser system of claim 19, furthercomprising a filter configured to remove amplified spontaneous emissionlight from the free-space amplified beam.
 23. The laser system of claim19, further comprising a beam pick-off and a detector configured todetect a portion of the free-space amplified beam reflected from thebeam pick-off.
 24. The laser system of claim 19, further comprising anoutput collimator disposed at an output end of the multi-clad gainfiber, wherein the output collimator is configured to produce acollimated free-space output beam having optical characteristicscomprising: a wavelength between approximately 1500 nm and approximately1600 nm; a pulse duration less than or equal to 10 nanoseconds; a dutycycle less than or equal to 1%; a pulse energy greater than or equal to100 nanojoules; and a peak power greater than or equal to 100 watts.